Electrocardiographic and genetic evaluation of giant jungle fowl, broilers, and their reciprocal crosses following unilateral bronchus occlusion.

Electrocardiography is useful as a noninvasive technique for detecting right ventricular hypertrophy in birds developing pulmonary hypertension (PH) and pulmonary hypertension syndrome (PHS, ascites). The objective of this study was to identify every aspect of the Lead II ECG wave form (amplitude or duration) that can be correlated with right ventricular hypertrophy [increased right:total ventricular weight ratios (RV:TV)] indicative of PH across a broad genetic background. Sham operations were conducted, or PH was induced by occluding one extrapulmonary primary bronchus in 14-d-old chicks produced from matings of broilers (B x B), Giant Jungle Fowl (J x J), and their reciprocal crosses (B x J and J x B). Standard three-lead electrocardiograms (ECG) were recorded on Days 28 and 42, and final necropsies were conducted to evaluate the incidence of ascites, confirm sex, and obtain ventricular weights for calculating RV:TV. Ascites did not develop in the J x J, and one each of the B x J and J x B chicks developed ascites; consequently, only data from birds that did not develop ascites were compared. Heart rate was recorded, and the following amplitudes and durations were measured or calculated for three consecutive wave cycles of the Lead II ECG: base of R to the peak of R (RbR), peak of R to base of S (RS), base of S to peak of R' (SR'), S, peak of R' to base of R' (R'R'b), and base of S to peak of T (ST). Differences between the ECG of sham and bronchus clamp groups were more prominent in B x B and B x J than in J x B, and bronchus occlusion did not affect the ECG, growth, or RV:TV ratios of J x J. In contrast, sex influences were more prominent in J x J and J x B than in B x J and B x B. These observations suggest a paternal pattern of inheritance for Lead II ECG wave forms, with crosses sired by broilers (B x B, B x J) exhibiting susceptibility to PH and few ECG differences related to sex, whereas crosses sired by Giant Jungle Fowl U x J, J x B) exhibited resistance to PH and numerous ECG differences related to sex.

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title: Independent and simultaneous unilateral occlusion of the pulmonary artery and extra-pulmonary primary bronchus in broilers.
abstract: Acutely tightening a snare around one pulmonary artery previously was shown to trigger a reversible ventilation-perfusion (V/Q) mismatch in broilers, as reflected by decreases in the partial pressure of oxygen in arterial blood (hypoxemia), accompanied by increases in the hydrogen ion concentration (acidosis) and partial pressure of carbon dioxide (hypercapnia). In the present study, snares were loosely implanted around the right pulmonary artery and the right extrapulmonary primary bronchus in anesthetized male broilers. These snares were tightened and released independently and then simultaneously to evaluate the possibility that directing the entire respiratory minute volume toward the left lung might attenuate the V/Q mismatch caused by forcing the entire cardiac output (CO) through the left lung. Fully reversible arterial blood hypoxemia, acidosis, and hypercapnia occurred when either snare was tightened independently. Presumably, tightening the bronchial snare restricted ventilation but not blood flow to the right lung, thereby permitting blood to perfuse poorly ventilated gas exchange surfaces. Simultaneously tightening both snares triggered arterial blood hypoxemia, acidosis, and hypercapnia similar to or greater in magnitude than the responses obtained by tightening the pulmonary artery snare independently. Tightening either snare independently or both snares simultaneously caused pulmonary arterial pressure to increase (pulmonary hypertension), and permanent obstruction of one bronchus in a separate experiment caused an increase in the right:total ventricular weight ratio, which is indicative of chronic pulmonary hypertension. The mean systemic arterial pressure decreased when the pulmonary artery snare was tightened independently or in combination with the bronchial snare, but not when the bronchial snare was tightened independently. The respiratory rate increased and the heart rate decreased when the pulmonary artery snare was tightened independently, but not when the bronchial snare was tightened independently or in combination with the pulmonary artery snare. These results demonstrate that the V/Q mismatch caused by forcing all the CO to perfuse one lung cannot be attenuated by simultaneously directing the entire respiratory minute volume toward the same lung.

title: Inheritance of carcass variables when giant jungle fowl and broilers achieve a common physiological body weight.
abstract: Ten chicks each from Giant Jungle Fowl (JF), broiler breeders (BB), and the respective F1 cross between them, were reared under typical broiler management practices until they reached a market weight of approximately 1,818 g. When individual birds reached market weight they were killed by CO2 asphyxiation and variables (length and weight) associated with organ, muscle, and skeletal growth were measured. Age to market weight demonstrated parental and heterotic effects. The JF had more deboned leg muscle and less Pectoralis major muscle than BB. Abdominal fat was higher in BB and showed positive heterosis. Organ weights were consistently lower for JF than BB. Positive heterosis was observed for spleen and pancreas, and negative heterosis was indicated for heart, liver, and lung. The digestive tract generally weighed less and was shorter in length for JF than for BB. Positive heterosis was observed for proventriculus and gizzard weight, and negative heterosis was noted for duodenum and jejunum lengths. Parental line differences were observed for most bone variables, including weight and length. Parental lines differed for femur breaking strength, but not for tibiotarsus breaking strength. A large negative heterotic effect was observed for tibiotarsus bone breaking strength.

title: Effect of chronic hypoxia on the pulmonary arterial blood pressure of the chicken.
abstract: BURTON, R. R., E. L. BESCH, AND A. H. SMITH. Efect of chronic hypoxia on the pulmonary arterial blood pressure of the chicken.  White Leghorn chickens hatched and living in a high-altitude environment of 12,500-ft elevation, had pulmonary arterial blood pressures approximately twice as great as found in chickens at sea level. The pulmonary arterial blood pressures were highly correlated with the relative right ventricular masses of the individual birds at all altitudes. The proportionality coefficients of this relationship in chickens were double those reported by others in cattle. In the female chicken it appears that each 1 mm Hg increase in the mean pulmonary arterial blood pressure above sea level control values results in a 41-mg increase in the right ventricular mass (hypertrophy). Inhalation of 95y0 oxygen and 57; carbon dioxide for 10 min had no apparent effect on this pulmonary arterial hypertension at high altitude, although acute hypoxia (asphyxia, by tracheal occlusion) produced a pulmonary arterial hypertension in sea-level birds. The occlusion of one major pulmonary artery produced a 6791, increase in the pulmonary arterial blood pressure in the unobstructed lung. Chronic hypoxia ( 12,500-ft elevation) produced a 47y0 reduction in the arterial oxygen tension and no significant changes in the arterial carbon dioxide tension and pH. Anesthesia at the surgical level in chickens results in an acute hypoxia and an acidosis. This hypoxic effect from the anesthesia was much less marked at high altitude. Pulmonary arterial blood pressures reached control values within 2 days after the high altitude-adapted animals were returned to sea level.

title: High altitude induced pulmonary hypertension and right heart failure in broiler chickens.
abstract: A total of 800 broiler chickens was studied; 400 at sea level, and 400 at an altitude of 3,300 m. Only the chickens raised in this latter condition showed an increased mean pulmonary arterial pressure (Ppa), weight of the right ventricle relative to that of both ventricles (RV/TV), haemoglobin concentrations, haematocrit value and red blood cell count. A high correlation between Ppa and R V/TV was found. Twenty per cent of the chickens raised at high altitude died with signs of right heart failure. The calculated Ppa in these birds was found to be greater than that of the high altitude birds which did not develop overt signs of cardiac insufficiency. These results indicate that some broiler chickens raised at high altitude develop right heart insufficiency secondary to pulmonary arterial hypertension.

title: Hypoxic ascites in broilers: a review of several studies done in Colombia.
abstract: In Bogotá, Colombia, broilers developed ascites due to pulmonary hypertension of hypoxic origin at 2638 m above sea level. This disease has tremendous economic impact in various countries of the world and is characterized by pulmonary hypertension, hypertrophy and hyperplasia of the right ventricle of the heart, increased hematocrit and hemoglobin values, and ascites. This entity appears to be influenced by management practices and by inability of broilers to adapt to high altitude.

title: Use of a hypobaric chamber as a model system for investigating ascites in broilers.
abstract: In a series of experiments, broilers were reared at simulated altitudes of 3000, 3500, and 5000 meters utilizing a hypobaric chamber. The purpose was to evaluate the chamber as a model for ascites syndrome and to further study the pathophysiology of this disease. Results show that this model can effectively reproduce the disease as it is seen in the field. Birds reared at the simulated altitude of 5000 meters had a statistically significant increase in EKG amplitude, packed cell volume, and heart-to-body-weight and lung-to-body-weight ratios when compared with controls reared at 366 meters. Additionally, there was a trend for birds dying of ascites to have larger-amplitude EKGs than survivors when reared at 5000 meters.

title: Morphometric and histologic changes in the pulmonary system of broilers raised at simulated high altitude.
abstract: Broilers were reared in conditions of hypobaric hypoxia (3500 m altitude) to investigate the development of pulmonary nodules in birds reared in hypobaric hypoxia and judged by clinical observation to be developing broiler pulmonary hypertension syndrome (BPHS); in unaffected birds reared in hypobaric hypoxia; and in birds reared at ambient atmospheric pressure. Gross pulmonary morphometric measurements, packed cell volume, electrocardiogram QRS amplitude and body weight also were compared among the three experimental groups. Results indicate that hypobaric hypoxia alone exercised little influence on the development of pulmonary nodules. Nodule numbers per section and nodule area per section were numerically greater in birds reared in hypobaric hypoxia, but there were no consistent significant differences in nodule numbers in birds which developed BPHS. As expected, absolute lung length, inter-rib distance and lung volume increased significantly with increasing age and size; but when these parameters were expressed as a function of body weight, they decreased with increasing age. Again, intergroup differences were inconsistent. Packed cell volume and electrocardiogram QRS amplitude were significantly increased in birds reared in hypobaric hypoxia.

title: Use of electrocardiographic analysis for investigation of ascites syndrome in broiler chickens.
abstract: This study was conducted (at high altitude [1969 meters]) to determine whether chicks predisposed to cardiac failure and ascites could be identified and followed during growout with non-invasive electrocardiographic (ECG) techniques. ECG recordings were made on 40 chicks at 1 week of age. All recordings were analyzed by quantifying the amplitude in millivolts of the R-, S-, and T-waves in each of the recordings. During the study, ascites-related mortality was 40%, with the majority of the deaths occurring between 5 and 8 weeks of age. Chicks exhibiting moderate-to-severe right ventricular hypertrophy, as identified by ECG analysis at 1 week of age, were predisposed to development of ascites. Thus, the variability in ascites-related mortality observed in field cases may be directly related to the number of predisposed chicks at the time of placement in the broiler house.

title: Evaluation of vectorelectrocardiographic analysis of young broiler chickens as a predictive index for susceptibility to ascites syndrome.
abstract: Vectorelectrocardiographic (VCG) analysis was performed on 50 male broiler chicks (1 week of age) before placement in a hypobaric chamber. During 5 weeks of exposure to hypobaric hypoxia (simulated altitude of 2900 m), all recorded mortality (38%) was due to the development of ascites syndrome. There was a positive correlation (r = 0.74, P less than 0.01) between the increment in the frontal plane mean resultant vector magnitude divided by body weight (designated as the cardiac index [CI]), with the severity of right ventricular enlargement. Chicks developing ascites syndrome had a greater CI (P less than 0.05) at 1 week of age when compared with chicks that did not develop the syndrome. Therefore, the CI calculated by VCG analysis recognizes right ventricular enlargement, suggesting that a pre-hatch or early post-hatch functional cardiac stress has occurred, predisposing the 1-week-old broiler chick to ascites syndrome. Application of the CI has a physiological index may prove useful in future studies targeted for selection of ascites syndrome resistance in broiler chickens.

title: Chronic unilateral occlusion of an extrapulmonary primary bronchus induces pulmonary hypertension syndrome (ascites) in male and female broilers.
abstract: Previously, it was demonstrated that acute (4 min) and chronic (12 d) occlusion of an extrapulmonary primary bronchus triggers pulmonary hypertension but not pulmonary hypertension syndrome (PHS, ascites) in broilers. The present study was conducted to determine whether a more prolonged period of bronchus occlusion causes PHS similar to that induced by clamping one pulmonary artery. Male and female broiler chicks, 14 to 18 d old, were anesthetized, the thoracic inlet was opened, and a silver clip was positioned to fully obstruct the left extrapulmonary primary bronchus (BRONCHUS CLAMP group) or the left pulmonary artery (PA-CLAMP group). Sham-operated chicks were anesthetized and the thoracic inlet was opened; however, neither the pulmonary artery nor the bronchus was clamped (SHAM group). An electrocardiogram (ECG) was obtained whenever clinical ascites became apparent in individual broilers, or prior to the final necropsy for broilers surviving to the end (Day 36) of the experiment. The right:total ventricular weight ratio (RV:TV) was evaluated as an index of pulmonary arterial pressure. Early post-surgical mortality (up to 21 d of age) was higher in the PA-CLAMP group (27% for males and females combined) than in the BRONCHUS CLAMP (10%) and SHAM (2%) groups. Cumulative ascites mortality (Days 22 to 36) also was higher in the PA-CLAMP group (86% for males, 77% for females) than in the BRONCHUS CLAMP (69% for males, 41% for females) and SHAM (23% for males, 0% for females) groups. Ascitic birds in all treatment groups had higher RV:TV ratios and more negative ECG Lead II S-wave amplitudes than nonascitic birds, reflecting the right ventricular hypertrophy and generalized ventricular dilation typically associated with PHS. These results demonstrate that unilateral bronchus occlusion is an effective experimental model for triggering ascites at a lower incidence than that obtained by occluding one pulmonary artery. Following the onset of pulmonary hypertension, the pathophysiological progression leading to ascites appears to be similar for broilers with either unilateral bronchus or pulmonary artery occlusion.

title: Evaluation of minimally invasive indices for predicting ascites susceptibility in three successive hatches of broilers exposed to cool temperatures.
abstract: Broilers from three consecutive hatches were exposed to cool temperatures to amplify the incidence of pulmonary hypertension syndrome (PHS, ascites). The largest apparently healthy individuals on Day 42 were evaluated using minimally invasive diagnostic indices [percentage saturation of hemoglobin with oxygen, hematocrit (HCT), heart rate, electrocardiogram (ECG) Lead II, body weight), then they were subjected to the ongoing pressures of fast growth and cool temperatures to determine which of these indices are predictive of the subsequent onset of PHS. Approximately 20% of the males and females evaluated on Day 42 subsequently developed PHS by Day 51. When data for all hatches were pooled and broilers that subsequently developed ascites were compared with those that did not (nonascitic), body weights, heart rates, and percentage saturation of hemoglobin with oxygen were lower on Day 42 for ascitic than for nonascitic males, and HCT was higher in ascitic males and females than in nonascitic males and females, respectively. Comparisons of the ECG Lead II wave amplitudes for all hatches pooled indicated that RS-wave amplitude was larger in ascitic than in nonascitic males, and that S-wave amplitude was more negative in ascitic males and females than in nonascitic males and females. Necropsies conducted on Day 51 revealed higher right:total ventricular weight ratios in ascitic than in nonascitic broilers, whereas normalizing the left ventricle plus septum weight for differences in body weight generated similar values for ascitic and nonascitic males and females, respectively. These results support a primary role for pulmonary hypertension but not cardiomyopathy in the pathogenesis of ascites triggered by cool temperatures. Values obtained for minimally invasive diagnostic indices on Day 42 also establish predictive thresholds that can be used to evaluate the PHS susceptibility of large and apparently healthy male and female broilers.

title: Electrocardiographic evaluation of broilers during the onset of pulmonary hypertension initiated by unilateral pulmonary artery occlusion.
abstract: Electrocardiography previously has been used as a noninvasive method for detecting cardiac hypertrophy associated with pulmonary hypertension syndrome (PHS, ascites). In the present study, 36 of 100 male broiler chicks were selected for inclusion in the experiment based on their hatch weight (> or = 40 g), Day 1 to 14 BW gain (upper 50% of population distribution), and the normalcy of their Day 14 electrocardiogram (ECG). On day 16, 10 chicks were assigned to the unoperated control group (CONTROL), sham operations were performed on 10 chicks (SHAM), and pulmonary hypertension was initiated by clamping the left pulmonary artery in 16 chicks (PA-CLAMP). Electrocardiogram leads I, II, III, and aVF were recorded daily until Day 27, when 6 of the 12 birds surviving in the PA-CLAMP group had developed clinical ascites. The right: total ventricular weight ratio (RV:TV) was higher and BW was lower in the PA-CLAMP group than in the CONTROL and SHAM groups on Day 27. The RS, R, and S wave amplitudes in lead II for the CONTROL and SHAM groups did not change, whereas in lead II for the PA-CLAMP group the S wave attained a more negative amplitude by Day 21, the RS wave attained a more negative amplitude by Day 22, and the R wave declined to a less positive amplitude by Day 23 when compared with presurgery values. Similar differences were observed for the RS and S waves for leads III and aVF. The mean electrical axis (MEA) and mean resultant vector (MRV) of the CONTROL and SHAM groups did not change; however the PA-CLAMP group the MEA rotated significantly from +3 degrees to -72 degrees and to -88 degrees on Days 14, 22 and 27, respectively, and the MRV amplitude increased from 0.052 to 0.108 mV and then to 0.179 mV on Days 14, 22, and 27, respectively. When data from all treatment groups were combined, higher absolute and BW-normalized RV:TV ratios were inversely correlated (r = 0.859 to -0.880) with increasingly negative S wave amplitudes in leads II and aVF. Higher absolute and BW-normalized RV:TV ratios were directly correlated (r = 0.786 to 0.789) with increasing MRV amplitudes. These ECG characteristics constitute accurate, noninvasive predictive criteria suitable for detecting cardiac changes occurring early during the onset of primary pulmonary hypertension.

title: The Response of Resistant and Susceptible Strains of Chickens and Their F1 and F2 Crosses to Subcutaneous Inoculations with Rous Sarcoma Virus
abstract: (1964, 1965) reported on the response of chorioallantoic membranes of two strains of chicken embryos and their F1- and F2-generation crossbreds to inoculations with Rous sarcoma virus. It was found that the “Giant Jungle Fowl” was resistant while the White Leghorn was susceptible and the F1 cross gave an intermediate response. Dhaliwal (1963) stated that the mechanism of resistance of the chorioallantoic membrane to Rous sarcoma virus was different from that of the embryo proper and the hatched chick or adult chicken. Beard (1958) mentioned that occasional retrogression had been observed in most types of tumors. In light of these observations, the present work was planned to investigate the response of the “Giant Jungle Fowl” and White Leghorn strains, their F1- and F2-generation crossbreds, to subcutaneous inoculations of Rous sarcoma virus in the wing web of five-week-old chickens. This mode of inoculation was chosen because …

title: Cardio-pulmonary function during acute unilateral occlusion of the pulmonary artery in broilers fed diets containing normal or high levels of arginine-HCl.
abstract: Cardio-pulmonary function was measured in male broilers reared on diets formulated to contain 1.5% arginine (NORMAL group) or 2.5% arginine (ARGININE group). A snare placed around the right pulmonary artery permitted acute shunting of the entire cardiac output (CO) through the left pulmonary artery, resulting in sustained increases in blood flow (BF) through the left lung in both groups. The unilateral increase in BF was accompanied by sustained increases in pulmonary arterial pressure (PAP) and pulmonary vascular resistance (PVR) in the NORMAL group. However, following initial transient increases in PAP and PVR in the ARGININE group, subsequent pulmonary vasodilation gradually reduced PVR, and thus PAP, in spite of the ongoing elevation of BF through the left lung. The capacity of the pulmonary vasculature in the ARGININE group to accommodate an increased BF at a normal PAP accounts for the previously reported lower incidence of pulmonary hypertension syndrome (PHS, ascites) in cold-stressed broilers fed supplemental dietary arginine. Hypoxemia and respiratory acidosis ensued rapidly in both groups after tightening the pulmonary artery snare, in spite of a compensatory increase in the respiratory rate. The gradual return of PVR and PAP to presnare levels in the ARGININE group did not eliminate the concurrent ventilation-perfusion mismatch caused by the increased rate of BF through the left lung. Tightening the pulmonary artery snare caused mean systemic arterial pressure (MAP) to drop from control levels of approximately 98 mm Hg to sustained hypotensive levels of approximately 65 mm Hg in both groups. This systemic hypotension was caused by decreases in CO and total peripheral resistance (TPR). The reduction in CO were caused by reduction in stroke volume (SV) rather than heart rate (HR), suggesting that acutely tightening the pulmonary artery snare increased PVR sufficiently to impede left ventricular filling. Accordingly, the maximum increment in PAP attainable by the right ventricle during acute increases in PVR apparently was inadequate to propel the entire CO through the pulmonary vasculature, setting the stage for the congestive right-sided pooling of blood routinely associated with PHS in broilers.

title: Physiologic and electrocardiographic changes occurring in broilers reared at simulated high altitude.
abstract: An experiment was conducted to determine whether differences in the electrocardiograms (EKGs) of broilers reared at simulated high altitude from the day of hatch can be used to predict which birds are developing ascites. In three replicate experiments, conducted with 100 broilers per replicate, birds were reared at a simulated altitude of 3000 meters or at ambient atmospheric pressure. Lead I, II, and III EKGs were obtained from all birds on days 0, 14, 28, and 42. No consistent significant differences were seen on day 0 in the amplitude of the R or S wave or total amplitude of the QRS complex when broilers that developed ascites while being reared at simulated high altitude were compared with unaffected birds reared at simulated high altitude and with birds reared at ambient atmospheric pressure. On days 14 and 28, the average amplitude of the S wave and the total amplitude of the QRS complex were significantly higher in the ascites group than in the two other groups. Packed cell volumes were significantly higher in birds reared at simulated high altitude at all sampling days (days 14, 28, and 42) than in those reared at ambient atmospheric pressure, and they were significantly higher in the ascites group on day 28 than in the two other groups. Birds in the ascites group weighed significantly less than the two other groups by day 14, and this trend persisted.

title: Role of Estrogen in Sex Difference of the Electrocardiogram of the Chicken.∗
abstract: The data demonstrate that amplitudes of R, S and RS of the ECG of normal hens are approximately half those of normal males. The effects of estrogen on the ECG of adult males were studied. The voltage of these waves of estrogenized males is decreased about 30 to 35%.

title: Broiler pulmonary hypertension syndrome. III. Commercial broiler strains differ in their susceptibility.
abstract: Broilers of 4 different commercial strains were kept during winter at an altitude of 1,350 m. The birds were slaughtered at weekly intervals and their relative right ventricular mass (pulmonary arterial pressure index = API values) determined. In addition, the incidence of ascites was recorded. Two of the strains suffered high losses from ascites, while the other 2 showed a certain degree of resistance. The former 2 groups had a higher mean API and a greater percentage of high API values in clinically normal birds than the other 2 groups. The group with the lowest incidence of ascites achieved the highest mean live mass at 51 days. There was also a decrease in mean API with age in clinically normal birds. There was no difference in the incidence of ascites between males and females.