A method of determining a photoplethysmography pulse amplitude ratio for use in automating a process for determining cardiac filling pressure non-invasively and, wherein the method is implemented on a device comprising a user interface and a microprocessor being communicatively coupled to each of an optical pulse volume sensing device and a pressure transducer, the method comprising the following method steps: analyzing a photoplethysmography signal having a pulse amplitude obtained from the optical pulse volume sensing device said analyzing being done to determine that a variation of a baseline of the photoplethysmography signal is within some standard deviation of its mean over a first predetermined time period before an expiratory effort or positive pressure inspiration; displaying a first instruction (410, 520) on the user interface to inform a user that a second instruction to initiate an expiratory effort or positive pressure inspiration will be displayed; displaying the second instruction (430, 530) on the user interface informing the user to begin an expiratory effort or positive pressure inspiration and to sustain the expiratory effort or positive pressure inspiration for a second predetermined period of time; obtaining the expiratory effort or positive pressure inspiration from the pressure transducer; comparing (450, 540) the expiratory effort or positive pressure inspiration to a predetermined goal range for expiratory effort or positive pressure inspiration and determining via an input of the pressure transducer if the expiratory effort or positive pressure inspiration does not meet the predetermined goal range within a third predetermined period of time; and displaying an indicator of the user's expiratory effort or positive pressure inspiration relative to the predetermined goal range on the user interface comprising indicating to the user that the data acquisition sequence is invalid when the expiratory effort or positive pressure inspiration does not meet the predetermined goal range within the third predetermined period of time; calculating a first average (A; 460) of the pulse amplitude of the photoplethysmography signal for a fourth predetermined period of time before the user ceases the expiratory effort or positive pressure inspiration; calculating a second average (B; 420)of the pulse amplitude of the photoplethysmography signal for a fifth period of time before an initiation of the expiratory effort or positive pressure inspiration; and calculating a pulse amplitude ratio (A/B; 470) of the first average of the pulse amplitude to the second average of the pulse amplitude. analyzing a photoplethysmography signal having a pulse amplitude obtained from the optical pulse volume sensing device said analyzing being done to determine that a variation of a baseline of the photoplethysmography signal is within some standard deviation of its mean over a first predetermined time period before an expiratory effort or positive pressure inspiration; displaying a first instruction (410, 520) on the user interface to inform a user that a second instruction to initiate an expiratory effort or positive pressure inspiration will be displayed; displaying the second instruction (430, 530) on the user interface informing the user to begin an expiratory effort or positive pressure inspiration and to sustain the expiratory effort or positive pressure inspiration for a second predetermined period of time; obtaining the expiratory effort or positive pressure inspiration from the pressure transducer; comparing (450, 540) the expiratory effort or positive pressure inspiration to a predetermined goal range for expiratory effort or positive pressure inspiration and determining via an input of the pressure transducer if the expiratory effort or positive pressure inspiration does not meet the predetermined goal range within a third predetermined period of time; and displaying an indicator of the user's expiratory effort or positive pressure inspiration relative to the predetermined goal range on the user interface comprising indicating to the user that the data acquisition sequence is invalid when the expiratory effort or positive pressure inspiration does not meet the predetermined goal range within the third predetermined period of time; calculating a first average (A; 460) of the pulse amplitude of the photoplethysmography signal for a fourth predetermined period of time before the user ceases the expiratory effort or positive pressure inspiration; calculating a second average (B; 420)of the pulse amplitude of the photoplethysmography signal for a fifth period of time before an initiation of the expiratory effort or positive pressure inspiration; and calculating a pulse amplitude ratio (A/B; 470) of the first average of the pulse amplitude to the second average of the pulse amplitude.