Abstract:
A congenital heart disease monitor utilizes a sensor capable of emitting multiple wavelengths of optical radiation into a tissue site and detecting the optical radiation after attenuation by pulsatile blood flowing within the tissue site. A patient monitor is capable of receiving a sensor signal corresponding to the detected optical radiation and calculating at least one physiological parameter in response. The physiological parameter is measured at a baseline site and a comparison site and a difference in these measurements is calculated. A potential congenital heart disease condition in indicated according to the measured physiological parameter at each of the sites or the calculated difference in the measured physiological parameter between the sites or both.

Description:
REFERENCE TO RELATED APPLICATION 
     The present application claims priority benefit under 35 U.S.C. §119(e) from U.S. Provisional Application No. 60/846,160, filed Sep. 20, 2006, entitled “Congenital Heart Disease Monitor,” which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Congenital heart disease (CHD) is relatively common, occurring in 5 to 10 of every 1,000 live births. Early diagnosis and treatment has improved outcomes in this population, but still a number of infants with CHD are sent home undiagnosed. Up to 30% of deaths due to CHD in the first year of life are due to such unrecognized cases. Several forms of CHD are the result of a patent ductus arteriosus (PDA). 
       FIG. 1  illustrates a fetal heart  102  and a portion of a fetal lung  104 . Prior to birth, the lung  104  is non-functional and fluid-filled. Instead, oxygenated blood is supplied to the fetus from gas-exchange in the placenta with the mother&#39;s blood supply. Specifically, oxygenated blood flows from the placenta, through the umbilical vein  106  and into the right atrium  122 . There, it flows via the foramen  124  into the left atrium  152 , where it is pumped into the left ventricle  150  and then into the aortic trunk  190 . Also, oxygenated blood is pumped from the right atrium  122  into the right ventricle  120  and directly into the descending aorta  140  via the main pulmonary artery  180  and the ductus arteriosus  130 . The purpose of the ductus arteriosus  130  is to shunt blood pumped by the right ventricle  120  past the constricted pulmonary circulation  110  and into the aorta  140 . Normally, the ductus arteriosus  130  is only patent (open) during fetal life and the first 12 to 24 hours of life in term infants. If the ductus arteriosus remains patent, however, it can contribute to duct-dependent congenital heart diseases, such as those described below. 
     Patent Ductus Arteriosus 
       FIG. 2  illustrates a neonatal heart  202  with a patent ductus arteriosus  230 . The ductus arteriosus frequently fails to close in premature infants, allowing left-to-right shunting, where oxygenated “red” blood flows from the aorta  240  to the now unconstricted pulmonary artery  210  and recirculates through the lungs  204 . A persistent patent ductus arteriosus (PDA) results in pulmonary hyperperfusion and an enlarged right ventricle  220 , which leads to a variety of abnormal respiratory, cardiac and genitourinary symptoms. 
     Persistent Pulmonary Hypertension in Neonates 
     As shown in  FIG. 2 , persistent Pulmonary Hypertension in Neonates (PPHN) is a neonatal condition with persistent elevation of pulmonary vascular resistance and pulmonary artery pressure. The pulmonary artery  210  that normally feeds oxygen depleted “blue” blood from the right ventricle  220  to the lung  204  is constricted. The back pressure from the constricted pulmonary artery  210  results in a right-to-left shunting of this oxygen depleted blood through the ductus arteriosus  230 , causing it to mix with oxygen rich “red” blood flowing through the descending aorta  240 . 
     Aortic Coarctation 
     Also shown in  FIG. 2 , coarctation of the aorta is a congenital cardiac anomaly in which obstruction or narrowing occurs in the distal aortic arch  290  or proximal descending aorta  240 . It occurs as either an isolated lesion or coexisting with a variety of other congenital cardiac anomalies, such as a PDA. If the constriction is preductal, lower-trunk blood flow is supplied predominantly by the right ventricle  220  via the ductus arteriosus  230 , and cyanosis, i.e. poorly oxygenated blood, is present distal to the coarctation. If the constriction is postductal, blood supply to the lower trunk is supplied via the ascending aorta  240 . 
     SUMMARY OF THE INVENTION 
     Once a problematic patent ductus arteriosus (PDA) is detected, closure can be effected medically with indomethacin or ibuprofen or surgically by ligation. Clinical symptoms of duct-dependent CHD, however, can vary on an hourly basis, and the required extended and inherently intermittent testing is difficult with current diagnostic techniques. These techniques include physical examination, chest x-ray, blood gas analysis, echocardiogram, or a combination of the above to detect, as an example, the soft, long, low-frequency murmur associated with a large PDA or, as another example, a retrograde flow into the main pulmonary artery. 
     As shown in  FIG. 2 , a right hand has blood circulating from the left ventricle  250  through the innominate artery  260 , which supplies the right subclavian artery (not shown). Because the innominate artery  260  is upstream from the ductus arteriosus  230 , the oxygen saturation value and plethysmograph waveform obtained from the right hand are relatively unaffected by the shunt and serve as a baseline or reference for comparison with readings from other tissue sites. Alternatively, a reference sensor can be placed on a facial site, such as an ear, the nose or the lips. These sites provide arterial oxygen saturation and a plethysmograph for blood circulating from the left ventricle  250  to the innominate artery  260 , which supplies the right common carotid artery (not shown), or to the left common carotid artery  265 . 
     Also shown in  FIG. 2 , either foot has blood supplied from the descending aorta  240 . A PDA  230  affects both the oxygen saturation and the blood flow in the descending aorta  240 . As stated above, the PDA  230  causes oxygen-depleted blood to be mixed with oxygen-rich blood in the descending aorta  240 . Because the descending aorta  240  supplies blood to the legs, the oxygen saturation readings at the foot will be lowered accordingly. That is, duct-dependent CHD may be manifested as a higher arterial oxygen saturation measured at a right hand tissue site (reference) and a lower oxygen saturation measured at a foot tissue site. 
     A PDA also allows a transitory left to right flow during systole, which distends the main pulmonary artery  280  as the result of the blood flow pressure at one end from the right ventricle and at the other end from the aortic arch  290 . A left-to-right flow through the shunt  230  into the distended artery  280  alters the flow in the descending aorta  240  and, as a result, plethysmograph features measured at either foot. Duct-dependent CHD, therefore, may also be manifested as a plethysmograph with a narrow peak and possibly a well-defined dicrotic notch at a hand baseline site and a broadened peak and possibly no notch at a foot site. 
     Further shown in  FIG. 2 , a left hand has blood circulating from the left ventricle through the left subclavian artery  270  that supplies the left arm. Because the left subclavian artery  270  is nearer a PDA  230  than the further upstream innominate artery  260 , it may experience some mixing of deoxygenated blood and an alteration in flow due to the PDA  230 . Duct-dependent CHD, therefore, may also be manifested as a reduced saturation and an altered plethysmograph waveform measured at a left hand tissue site as compared with the right hand baseline site, although to a lesser degree than with a foot site. 
       FIG. 3  illustrates a patient monitoring system  300 , which provides blood parameter measurements, such as arterial oxygen saturation, and which can be adapted as an advantageous diagnostic tool for duct-dependent CHD. The patient monitoring system  300  has a patient monitor  302  and a sensor  306 . The sensor  306  attaches to a tissue site and includes a plurality of emitters  322  capable of irradiating a tissue site  320  with differing wavelengths of light, such as the red and infrared wavelengths utilized in pulse oximeters. The sensor  306  also includes one or more detectors  324  capable of detecting the light after attenuation by the tissue  320 . A sensor is disclosed in U.S. application Ser. No. 11,367,013, filed on Mar. 1, 2006, titled Multiple Wavelength Sensor Emitters, which is incorporated by reference herein. Sensors that attach to a tissue site and include light emitters capable of irradiating a tissue site with at least red and infrared wavelengths are disclosed in one or more of U.S. Pat. Nos. 5,638,818, 5,782,757, 6,285,896, 6,377,829, 6,760,607 6,934,570 6,985,764 and 7,027,849, incorporated by reference herein. Moreover, low noise optical sensors are available from Masimo Corporation, Irvine, Calif. 
     As shown in  FIG. 3 , the patient monitor  302  communicates with the sensor  306  to receive one or more intensity signals indicative of one or more physiological parameters and displays the parameter values. Drivers  310  convert digital control signals into analog drive signals capable of driving sensor emitters  322 . A front-end  312  converts composite analog intensity signal(s) from light sensitive detector(s)  324  into digital data  342  input to the DSP  340 . The DSP  340  may comprise a wide variety of data and/or signal processors capable of executing programs for determining physiological parameters from input data. In an embodiment, the DSP executes the CHD screening and analysis processes described with respect to  FIGS. 7-9 , below. 
     The instrument manager  360  may comprise one or more microcontrollers controlling system management, such as monitoring the activity of the DSP  340 . The instrument manager  360  also has an input/output (I/O) port  368  that provides a user and/or device interface for communicating with the monitor  302 . In an embodiment, the I/O port  368  provides threshold settings via a user keypad, network, computer or similar device, as described below. 
     Also shown in  FIG. 3  are one or more devices  380  including a display  382 , an audible indicator  384  and a user input  388 . The display  382  is capable of displaying indicia representative of calculated physiological parameters such as one or more of a pulse rate (PR), plethysmograph (pleth) morphology, perfusion index (PI), signal quality and values of blood constituents in body tissue, including for example, oxygen saturation (SpO 2 ), carboxyhemoglobin (HbCO) and methemoglobin (HbMet). The monitor  302  may also be capable of storing or displaying historical or trending data related to one or more of the measured parameters or combinations of the measured parameters. The monitor  302  may also provide a trigger for the audible indictor  384  for beeps, tones and alarms, for example. Displays  382  include for example readouts, colored lights or graphics generated by LEDs, LCDs or CRTs to name a few. Audible indicators  384  include, for example, tones, beeps or alarms generated by speakers or other audio transducers to name a few. The user input device  388  may include, for example, a keypad, touch screen, pointing device, voice recognition device, or the like. 
     A patient monitor is disclosed in U.S. application Ser. No. 11,367,033, filed on Mar. 1, 2006, titled Noninvasive Multi-Parameter Patient Monitor, incorporated by reference herein. Pulse oximeters capable of measuring physiological parameters including SpO 2 , pleth, perfusion index and signal quality are disclosed in one or more of U.S. Pat. Nos. 6,770,028, 6,658,276, 6,157,850, 6,002,952, and 5,769,785, incorporated by reference herein. Moreover, pulse oximeters capable of reading through motion induced noise are available from Masimo Corporation, Irvine, Calif. 
     A congential heart disease (CHD) monitor advantageously utilizes a patient monitor capable of providing multiple-site blood parameter measurements, such as oxygen saturation, so as to detect, for example, hand-foot oxygen saturation differences associated with a PDA and related CHD. 
     One aspect of a CHD monitor is a sensor, a patient monitor and a DSP. The sensor is configured to emit optical radiation having a plurality of wavelengths into a tissue site and to detect the optical radiation after attenuation by pulsatile blood flowing within the tissue site. The monitor is configured to drive the sensor, receive a sensor signal corresponding to the detected optical radiation and to generate at least one of a visual output and an audio output responsive to the sensor signal. The DSP is a portion of the patient monitor and is programmed to derive a physiological parameter from sensor data responsive to the sensor signal. The physiological parameter is measured at a baseline tissue site and a comparison tissue site. The outputs indicate a potential CHD condition according to a difference between the physiological parameter measured at the baseline tissue site and the physiological parameter measured at the comparison tissue site. 
     Another aspect of a CHD monitor is a congenital heart disease screening method providing a patient monitor and corresponding sensor. The sensor is capable of emitting optical radiation having a plurality of wavelengths into a tissue site and detecting the optical radiation after attenuation by pulsatile blood flowing within the tissue site. The patient monitor is capable of receiving a sensor signal corresponding to the detected optical radiation and calculating a blood-related physiological parameter. The physiological parameter is measured at a baseline tissue site and a comparison tissue site. The measured physiological parameter at the baseline tissue site and at the comparison tissue site are compared. A potential CHD condition is indicated based upon the comparison. 
     A further aspect of a CHD monitor is a detection method determining a plurality of metrics responsive to sensor data derived from a plurality of tissue sites on an infant, testing the metrics with respect to predetermined rules and thresholds, and outputting diagnostics responsive to the test results. The metrics are at least one of a physiological parameter measurement, a cross-channel measurement and a trend. The diagnostics are responsive to the likelihood of congenital heart disease. 
     Yet another aspect of a CHD monitor comprises a patient monitor, a pre-processor means, an analyzer means and a post-processor means. The patient monitor is configured to receive sensor data from at least one optical sensor attached to a plurality of tissue sites on an infant. The pre-processor means is for deriving at least one metric from the sensor data. The analyzer means is for testing the at least one metric according to at least one rule. The post-processor means is for generating diagnostics based upon results of the testing The at least one rule defines when the at least one metric indicates a potential CHD condition in the infant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a fetal heart depicting a ductus arteriosis; 
         FIG. 2  is an illustration of a neonatal heart depicting a patent ductus arteriosis (PDA); 
         FIG. 3  is a general block diagram of a patient monitoring system adapted for congenital heart disease (CHD) detection; 
         FIG. 4  is an illustration of a single patient monitor utilized for CHD detection; 
         FIG. 5  is an illustration of multiple patient monitors utilized for CHD detection; 
         FIG. 6  is an illustration of a single patient monitor and multi-site sensor utilized for CHD detection; 
         FIGS. 7A-B  is a flow diagram of a CHD screening embodiment; 
         FIG. 8  is a detailed block diagram of a CHD analyzer embodiment; and 
         FIG. 9  is a detailed block diagram of a preprocessor embodiment for a CHD analyzer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 4  illustrates CHD detection utilizing a single patient monitor  410  and corresponding sensor  420 . In general, the monitor  410  provides a display or other indicator that directs a caregiver or other user to attach the sensor  420  to an initial tissue site for a first measurement and then to one or more other tissue sites for additional measurements. This procedure is described in further detail with respect to  FIGS. 7A-B , below. For example, in a Phase I configuration  401 , the sensor  420  is attached to a neonate&#39;s right hand so that the monitor  410  generates baseline site measurements. In a Phase II configuration  402 , the sensor  420  is attached to a neonate&#39;s foot so that the monitor  410  generates comparison site measurements. In an optional Phase III configuration  403 , the sensor  420  is attached to a neonate&#39;s left hand generating measurements at an additional comparison site. During each phase  401 - 403 , the monitor  410  takes measurements for a length of time sufficient to determine user-selected parameters, which includes SpO 2  and may include PR, PI, signal quality, pleth morphology, other blood parameters such as HbCO and HbMET, and trends over a selected time interval for any or all of these parameters. In an embodiment, baseline right-hand measurements are made first, followed by measurements at either foot, followed by optional left-hand measurements. In other embodiments, the phase-order of measurements can be user-selected and can be in any order and can include or exclude either the foot or the left-hand measurements. 
     In an embodiment, a monitor-determined time or user-selectable timer defines how long each site measurement is made, and a monitor display and/or audible indicator signals the user when to switch sensor sites. In an embodiment, a user defines time intervals or times-of-day for making repeat measurement cycles so as to obtain site difference trends. A monitor display and/or audible indicator signals the user when to begin a measurement cycle. 
       FIG. 5  illustrates CHD detection utilizing multiple patient monitors  510 - 520  and corresponding sensors  530 - 540 . In an embodiment, a first monitor  510  and first sensor  530  provide measurements from a right-hand tissue site. A second monitor  520  and second sensor  540  provide measurements from a foot tissue site. An interface cable  550  or wireless link provides communications between the monitors  510 - 520 . For example, the monitors  510 - 520  can communicate respective measurements via RS-232, USB, Firewire or any number of standard wired or wireless communication links. In an embodiment, one monitor, such as the baseline right-hand monitor  510  acts as the master and the comparison (e.g. foot) monitor  520  acts as a slave. The master monitor  510  generates the baseline measurements, transfers the comparison measurements from the slave monitor  520 , calculates the comparison parameters, such as oxygen saturation differences, displays the comparison parameters, calculates alarm conditions based upon the measured and comparison parameters and generates alarms accordingly. 
     In other embodiments, the comparison site (e.g. foot or left-hand) monitor  520  is the master and the baseline (right-hand) monitor  510  is the slave. In yet another embodiment, there are three networked monitors corresponding to right-hand, left-hand and foot sites, with one monitor acting as a master and the other monitors acting as slaves. The master monitor, in this example, calculates oxygen saturation differences for each pair of sites and generates alarms accordingly. 
       FIG. 6  illustrates CHD screening utilizing a single CHD patient monitor  610  and a corresponding multi-site sensor  620 . In an embodiment, the multi-site sensor  620  has two sensor heads  622 - 624  and a common sensor cable  628  for communication with the monitor  610 . One sensor head  622  is attached to a baseline tissue site, e.g. a right-hand and another sensor head  624  is attached to a comparison tissue site, e.g. either a foot or a left-hand. In another embodiment, a third sensor head  626  is available for attachment to a second comparison site, e.g. a left-hand. A multiple site patient monitor is disclosed in U.S. Pat. No. 6,334,065 issued Dec. 25, 2001 titled Stereo Pulse Oximeter which is assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein. 
       FIGS. 7A-B  illustrate a CHD screening process  700  corresponding to a single monitor CHD detection embodiment, such as described with respect to  FIG. 4 , above. In general, the process  700  is described with respect to user actions  701  and monitor responses  702  and, likewise, monitor prompts  702  and user responses  701 . In particular, once the monitor enters a CHD detection mode, the monitor prompts a user to attach the sensor successively to two or more tissue sites. In this manner, the monitor can compute baseline and comparison site measurements and calculate site differences, such as in oxygen saturation, which tend to predict the likelihood or unlikelihood of CHD. In an embodiment, the monitor  702  communicates instructions to the user  701  or otherwise prompts the user with display messages. Alternatively, or in addition to display messages, the monitor  702  can prompt the user via audio messages or indicators, visual indicators such as panel lights or a combination of the above. In an embodiment, the user  701  can trigger the monitor  702  or otherwise respond to monitor  702  prompts via a panel-mounted push button. Alternatively, or in addition to a push button, the user  701  can trigger the monitor  702  or otherwise respond to the monitor  702  via touch screen, touch pad, keyboard, mouse, pointer, voice recognition technology or any similar mechanism used for accomplishing a computer-human interface. 
     As shown in  FIG. 7A , a user  701  initiates CHD screening  705  and the monitor  702  enters a CHD detection mode  710  in response. The monitor  702  then prompts the user  701  to attach a sensor to a baseline site  715 . In response, the user  701  attaches a sensor to a first tissue site  720 , such as a neonate&#39;s right hand, and pushes a button  725  to trigger the monitor to take baseline sensor measurements  730 . The monitor  702  displays the resulting baseline measurements  732  and prompts the user  701  to reattach the sensor to a comparison site  735 . In response, the user  701  removes the sensor and reattaches it to a second tissue site  740 , such as either of a neonate&#39;s feet, and pushes a button  745  to trigger the monitor  702  to take comparison sensor measurements  750 . The monitor  702  displays the resulting comparison site measurements  755 . 
     As shown in  FIG. 7B , after taking baseline site and comparison site measurements, the monitor  702  determines if a third site measurement is to be taken  760 . If so, the monitor  702  prompts the user  701  to reattach the sensor to an additional comparison site  765 . In response, the user  701  removes the sensor and reattaches it to a third tissue site  770 , such as a neonate&#39;s left-hand, and pushes a button  775  to trigger the monitor  702  to take additional comparison site measurements  780 . The monitor  702  then displays the resulting measurements  785 . The monitor  702  determines if trend measurements are being made  787 . If so, then after a predetermined delay the monitor  702  prompts the user to re-attach the sensor at the baseline site  715  ( FIG. 7A ) to begin an additional series of measurements  730 - 785 . 
     Also shown in  FIG. 7B , after all site measurements are taken, the monitor  702  calculates the measurement differences between the baseline and comparison site(s)  790 , calculates trends in measurements and measurement differences  790  and displays the results  792 . The monitor  702  then determines whether any site measurements, site measurement differences or trends are outside of preset limits  794 . If limits are exceeded, the monitor generates visual and/or audio indicators of a potential CHD condition  796 . For example, an audio alert or alarm of a potential CHD condition may be a low-level intermittent beep so as to indicate a diagnostic result and not be confused with other urgent care alarms. In one embodiment, if neonatal SpO 2  measurements from both a right hand and a foot are less than about 95% or a hand-foot difference is greater than about ±3%, the monitor generates one or more indicators alerting a caregiver that a potential CHD condition exists. 
       FIG. 8  illustrates a CHD analyzer  800  that executes in the DSP  340  ( FIG. 3 ) and indicates a potential CHD or lack thereof. The CHD analyzer  800  is advantageously responsive to multiple channels of sensor data  801  so as to generate CHD diagnostics  803 . In an embodiment, the CHD analyzer  800  executes the CHD screening process described with respect to  FIGS. 7A-B , above, receiving sensor data  342  ( FIG. 3 ) derived from one tissue site at a time. In another embodiment, the CHD analyzer  800  receives sensor data  342  ( FIG. 3 ) derived from two or more sensor sites at a time, such as described with respect to  FIGS. 5-6 , above. The diagnostic output  803  can be used, for example, to generate displays or indicators useful for grading a neonate with respect to a potential CHD condition and the severity of that condition. In an embodiment, an instrument manager  360  ( FIG. 3 ) convert CHD diagnostics  803  via a display driver  362  ( FIG. 3 ) and an audio driver  364  ( FIG. 3 ) into one or more displays  382  ( FIG. 3 ) and audible indicators  384  ( FIG. 3 ) for use by a physician, clinician, nurse or other caregiver. 
     In an embodiment, the CHD analyzer  800  has a pre-processor  900 , a metric analyzer  820 , a post-processor  830  and a controller  840 . The pre-processor  900  has sensor data inputs  801  from one or more sensor channels, such as described with respect to  FIGS. 4-6 , above. The pre-processor  900  generates metrics  822  that may include, for example, physiological parameters, waveform features, and cross-channel comparisons and trends, as described in further detail with respect to  FIG. 9 , below. 
     As shown in  FIG. 8 , the metric analyzer  820  is configured to test metrics  822  and communicate the test results  824  to the post-processor  830  based upon various rules applied to the metrics  822  in view of various thresholds  826 . As an example, the metric analyzer  820  may communicate to the post-processor  830  when a parameter measurement increases faster than a predetermined rate, e.g. a trend metric exceeds a predetermined trend threshold. 
     Also shown in  FIG. 8 , the post processor  830  inputs test results  824  and generates CHD diagnostic outputs  803  based upon output definitions  832 . For example, if the test result is that a trend metric exceeds a trend threshold, then the output definition corresponding to that test result may be to trigger an audible alarm. Thresholds, rules, tests and corresponding outputs are described in further detail with respect to TABLE 1, below. 
     Further shown in  FIG. 8 , the controller  840  has an external communications port  805  that provides predetermined thresholds, which the controller  840  transmits to the metric analyzer  820 . The controller  840  may also provide metric definitions  824  to the pre-processor  900  and define outputs  832  for the post-processor  830 . 
     In an embodiment, CHD screening grades a neonate with respect to a likelihood of a CHD condition utilizing green, yellow and red indicators. For example, a green panel light signals that no metric indicates a potential CHD condition exists. A yellow panel light signals that one metric indicates a potential CHD condition exists. A red panel light signals that more than one metric indicates that a potential CHD condition exists. In an embodiment, the CHD analyzer  800  provides a diagnostic output  803  according to TABLE 1, below. The terms Sat xy , ΔSat xy  and Δt listed in TABLE 1 are described with respect to  FIG. 9 , below. Various other indicators, alarms, controls and diagnostics in response to various combinations of parameters and thresholds can be substituted for, or added to, the rule-based outputs illustrated in TABLE 1. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 CHD Analyzer Rules and Outputs 
               
             
          
           
               
                 RULE 
                 OUTPUT 
               
               
                   
               
               
                 If Sat &gt; Sat limit threshold (all channels); 
                 Then illuminate 
               
               
                  Sat xy  &lt; Sat xy  limit threshold (all cross-channels); and 
                 green indicator. 
               
               
                  ΔSat xy /Δt &lt; Sat xy  trend threshold (all cross-channels). 
               
               
                 If Sat &lt; Sat limit threshold (any channel); 
                 Then illuminate 
               
               
                  Sat xy  &gt; Sat xy  limit threshold (any cross-channel); or 
                 yellow 
               
               
                  ΔSat xy /Δt &gt; Sat xy  trend threshold (any cross-channel). 
                 indicator 
               
               
                 If Sat &lt; Sat limit threshold (any channel); and 
                 Then illuminate 
               
               
                  Sat xy  &gt; Sat xy  limit threshold (any cross-channel). 
                 red indicator 
               
               
                 If Sat &lt; Sat limit threshold (any channel); and 
                 Then illuminate 
               
               
                  ΔSat xy /Δt &gt; Sat xy  trend threshold (any cross-channel). 
                 red indicator 
               
               
                   
               
             
          
         
       
     
       FIG. 9  illustrates a preprocessor embodiment  900  that inputs sensor data  801  derived from one or more tissue sites and outputs metrics  822 . The preprocessor  900  has a parameter calculator  910 , a waveform processor  920 , a cross-channel calculator  930  and a trending function  940 . The parameter calculator  910  outputs one or more physiological parameters derived from pulsatile blood flow at a tissue site. These parameters may include, as examples, arterial oxygen saturation (SpaO 2 ), venous oxygen saturation (SpvO 2 ), PR and PI to name a few. In an embodiment, the parameter calculator  910  generates one or more of these parameters for each sensor data channel. The waveform processor  920  extracts various plethysmograph features for each data channel. These features may include, for example, the area under the peripheral flow curve, the slope of the inflow phase, the slope of the outflow phase, the value of the end diastolic baseline and the size and location of the dicrotic notch. The cross-channel calculator  930  generates cross-channel values, such as Sxy=SpO 2 (baseline site)−SpO 2 (comparison site). In an embodiment, the calculator  930  can also generate same-channel values, such as SpaO 2 −SpvO 2  from the same sensor site. The trending function  940  calculates trends from the parameter calculator  910 , the waveform processor  920  or the cross-channel calculator  930 . The trending function  940  stores historical values and compares these with present values. This comparison may include Δp/Δt, the change in a parameter over a specified time interval, which may also be expressed as a percentage change over that interval. An example is ΔSat xy /Δt, the change in the oxygen saturation difference between two tissue sites over a specified time interval. 
     Although described above with respect to optical sensor inputs responsive to pulsatile blood flow, in an embodiment, the CHD monitor may include sensor inputs and corresponding algorithms and processes for other parameters such as ECG, EEG, ETCO 2 , respiration rate and temperature to name a few. Although a CHD analyzer is described above as a program executed by a patient monitor DSP, the CHD analyzer can be, in whole or in part, hardware, firmware or software or a combination functioning in conjunction with or separate from the DSP. Further, the CHD analyzer can be configured, in whole or in part, as logic circuits, gate arrays, neural networks or an expert system, as examples. In an embodiment, a CHD monitor, such as described above, for example, as incorporating a patient monitor, CHD analyzer and corresponding CHD screening process, is marketed with instructions on grading a neonate, infant or patient with respect to the likelihood of a CHD condition. 
     A congential heart disease monitor has been disclosed in detail in connection with various embodiments. These embodiments are disclosed by way of examples only and are not to limit the scope of the present invention, which is defined by the claims that follow. One of ordinary skill in the art will appreciate many variations and modification.