Pulmonary gas exchange during intermittent ventilation in the American alligator.

The present study characterized pulmonary gas exchange in the American alligator, Alligator mississipiensis during ventilation and apnea at a body temperature (Tb) of 25 degrees C. Pulmonary gas exchange parameters were measured on a breath-by-breath basis utilizing a computer-assisted data acquisition system. In addition, paired blood samples were analyzed from left and right atrium during ventilation and voluntary apneas (1, 2, 5 and 10 min). Measurements of lung PO2 and PCO2 indicated that as apnea progressed, CO2 flux into the lung decreased rapidly while O2 was continuously removed at a constant and steady rate. The reduction in VCO2 resulted in a decrease in R (less than 0.4). Blood gas measurements indicated that the pulmonary arterial-pulmonary venous PCO2 difference, (Ppa-Ppv)CO2 was 4.9 +/- 0.9 mmHg during ventilation, decreased and became negative within 2 min of apnea, reaching -3.9 +/- 0.6 mmHg after 10 min. It is postulated that during apnea the Haldane effect accounts for both the blood gas behavior across the lung and insures a continued CO2 flux into the lung during apnea.

Relationship between respiratory state and intracardiac shunts in turtles.

Injection of radioactively labeled microspheres and blood O2 analysis from central vascular sites was utilized to assess intracardiac shunts in the unanesthetized and unrestrained turtle, Pseudemys scripta, at 15 degrees C. Both methods indicated a simultaneously occurring right-to-left (R-L) and left-to-right (L-R) shunt during ventilation and apnea. During ventilation, the O2 method estimated a R-L shunt of 24%. In contrast, injection of microspheres during ventilation estimated a R-L shunt of 65%, which was significantly greater than the value determined from the O2 method. During apnea, both methods indicated a significantly larger R-L shunt. Estimates of the R-L shunt from O2 analysis were between 60 and 90% of the venous return. The R-L shunt estimated from the O2 content of left aortic arch blood was significantly greater than the value determined from right aortic arch blood. During apnea, the microsphere method estimated a R-L shunt of 79%, which was in the intermediate range calculated by the O2 method using two aortic arches. Our results verify previous reports of significant differences in R-L shunt levels between ventilation and apnea during the normal ventilatory cycle of turtles.

Oxygen binding in alligator blood related to temperature, diving, and "alkaline tide".

Blood of Alligator mississippiensis has a relatively high O2 affinity, the half-saturation O2 tension (P50) = 24.5 Torr at pH 7.495, the arterial, normocapnic pH at 25 degrees C. Although the overall temperature sensitivity of P50 at 15, 25, and 35 degrees C and constant pH is low, the effect on P50 almost doubles when measured at the in vivo pH of each temperature (delta Happ = -24 and -47 kJ/mol, respectively). The CO2 Bohr effect (theta CO2 = -0.95) is 5.5 times greater than the fixed acid Bohr effect (theta FA), and the Haldane effect is small (approximately 0.03 pH units). The relatively high O2 affinity may ensure efficient utilization of the lung O2 reserve during breath holding and diving, whereas its pronounced in vivo temperature sensitivity may be adaptive to the high temperature quotients of the organismic O2 requirement. The large difference between theta CO2 and theta FA will favor constancy in blood O2 affinity in the face of large activity-induced increases in blood lactate and pronounced feeding-induced alkaloses. These "alkaline tides," which result from an exchange of plasma Cl- for HCO-3 across the gut wall, appear to be only slightly compensated by increased blood CO2 tensions. The results are additionally discussed in terms of allosteric modulation of hemoglobin-O2 affinity in crocodilians.

Oxygen binding functions of blood and hemoglobin from the Chinese pangolin, Manis pentadactyla: possible implications of burrowing and low body temperature.

We measured O2 equilibria of adult blood and of 'stripped' (cofactor-free) hemolysates from adult and newborn Manis pentadactyla, in order to assess the implications of the burrowing habit and the low deep-core temperature in pangolins, and to discern the mechanisms for maternal-fetal O2 transfer. At pH 7.4 and body temperature (33 degrees C) the blood O2 affinity was significantly higher than in similarly sized non-burrowing, 'normothermic' mammals (P50 = 21 and 33 mm Hg, respectively) indicating an adaptation to hypoxic burrow conditions. This difference is not attributable to a higher intrinsic O2 affinity in the pangolin Hb or to significant differences in its sensitivity to temperature and erythrocytic 2,3 diphosphoglycerate (DPG), but tallies with lower DPG/Hb ratios than generally found in mammals. Stripped adult and newborn hemolysates show similar O2 affinities and pH and DPG sensitivities, but reveal a specific adult Hb that develops after birth, in sharp contrast with the ontogenetic changes in other mammals where specific fetal Hbs are lost after birth.

Influence of temperature on the CO2 dissociation curve of the turtle Pseudemys scripta.

Carbon dioxide dissociation curves were constructed for blood of Pseudemys scripta. These were shifted by temperature and CCO2 was inverse to temperature at common PCO2. CO2 capacitance coefficients for oxygenated and deoxygenated blood (beta oxy, beta deoxy) were inverse to temperature at reported in vivo arterial PCO2's as was the Haldane effect. Data for in vivo PCO2 and Hb saturation of pulmonary arterial and venous blood allowed determination of effective beta which closely reflected values of beta oxy and beta deoxy at different temperatures. This indicates an influence of curve shape on beta eff at in vivo PCO2's. A high degree of correlation was found between air convection requirement (liters of gas ventilated per mmol CO2 produced) and beta eff at different temperatures. The inverse relationship between beta eff and temperature strongly influenced perfusive conductance of CO2 (Gperf = Vb X beta) and contributes to the temperature-independent stability of ventilatory to perfusive conductance ratio and the CO2 content of the animal. The influence of variable curve shape and Haldane effects must be considered as determinants of beta eff in the quantitative assessment of CO2 transport in this species.

Distribution of ventilation in American alligator Alligator mississippiensis.

The regional distribution of ventilation in the multicameral lung of spontaneously ventilating alligators (Alligator mississippiensis) was studied with 133Xe scintigraphy. Frequent gamma camera images of 133Xe washin and washout were obtained and processed to allow evaluation of regional ventilation. Washin of 133Xe to equilibrium occurred in three to four breaths in anterior, central, and posterior compartments. Washin was most rapid in the posterior compartment and slowest in the anterior. The structure of the lungs and distribution of ventilation of inspired gas is consistent with the rapid radial spread of gas through a parallel arrangement of lung units surrounding the central intrapulmonary bronchus. Washout to equilibrium of 133Xe from all compartments occurred within three to four breaths. This rapid washin and washout of gas to all parts of the lung stands in contrast to the lungs of turtles and snakes, in which the caudal air sacs are relatively poorly ventilated.

The effect of pH on the hypothermic ventricular fibrillation threshold.

During cardiac operations using hypothermia, the pH measured at 37 degrees C (and corrected to the patient's body temperature) is generally kept at 7.40. However, ectotherms (cold-blooded animals) regulate pH alkaline of 7.40 as temperature falls, e.g., pH 7.58 at 25 degrees C. Hypothermia and acidosis increase the propensity for ventricular fibrillation (VF). This study was undertaken to determine which scheme of pH regulation during hypothermia provided the highest level of cardiac electrical stability. Eleven dogs underwent median sternotomy and implantation of right ventricular and limb electrodes, aortic and central venous pressure catheters, and a probe to measure pulmonary artery blood temperature. To determine the VF threshold, a programmable stimulator was used to find the minimum current needed to produce VF by sweeping the vulnerable period of the cardiac cycle. The animals were divided into two groups for pH management: eight in the clinical scheme (pH 7.4) and seven in the ectothermic scheme, where pH varied with temperature. Control values were recorded prior to cooling and then repeated when core cooling had lowered the temperature to 25 degrees C. In the clinical group, the VF threshold decreased from 23.1 +/- 4.1 mA at 37 degrees C to 17.0 +/- 3.4 mA at 25 degrees C (p = 0.002); in the ectothermic group, the VF threshold was unchanged by hypothermia (23.7 +/- 3.2 to 22.8 +/- 2.8 mA). Heart rate and arterial and central venous pressures were not different between the groups at either temperature. Corrected arterial pH and PCO2 were unchanged from control in the clinical group at 25 degrees C (pH 7.40 +/- 0.01, arterial PCO2 34 +/- 2 torr), whereas arterial PCO2 was maintained at 20 +/- 1 torr to achieve pH 7.59 +/- 0.01 in the ectothermic group. Five of the eight dogs in the clinical group had spontaneous VF while cooling, as compared to one of the seven dogs in the ectothermic group. These studies demonstrate that allowing the corrected pH to rise with hypothermia and remain alkalotic relative to pH 7.4 improves the electrical stability of the heart during hypothermia, as evidenced by the VF threshold at 25 degrees C. Since the ectothermic scheme increases the electrical stability of the heart, it could decrease the incidence of VF during hypothermia and decrease the temperature at which VF occurs during hypothermic cardiopulmonary bypass.

Metabolic and acid-base changes during selection of warmer water by cold-acclimated fish.

Largemouth bass (Micropterus salmoides) acclimated to 3 degrees C were placed in a thermal gradient. The bass selected the final thermal preferendum of 28 degrees C in about 18 h. The movement into warmer water was initially rapid but became progressively slower. 2) Other bass were acclimated to 8 degrees C, cannulated in the dorsal aorta, and placed in a temperature-controlled chamber. Oxygen uptake, blood pH, and total CO2 were measured as the chamber temperature was increased to 28 degrees C following a time course similar to that followed by bass in the gradient. 3) Oxygen uptake was always elevated above the resting level, and this elevation increased as higher temperatures were encountered. 4) Just prior to placement in the chamber the pH of the arterial blood was 7.98 +/- 0.05 (mean +/- SE). As the temperature was increased neither the pH nor the total CO2 content of the blood exhibited major changes. At temperatures between 26 and 28 degrees C, the pH (8.01 +/- 0.03) was about 0.3 pH units above predicted normal values. 5) During the return to the final thermal preferendum fish experience overall metabolic rates and extracellular acid-base levels that deviate progressively farther from normal resting levels. Neither factor appears likely to be the major determinant of the behavioral response.

Studies of the ideal [H+] for perfusional preservation.

The neutral point of water, being a function of its dissociation constant, is temperature dependent. This is also true of protein-buffered solutions such as perfusates. In organ preservation these facts have been long ignored and, as a result, perfusions have been carried out in a relatively acidotic environment. These studies evaluated the effects of correcting the pH partially or completely for the level of hypothermia involved in perfusional preservation. The findings both in rabbits and dogs were that a pH of 7.4 (measured at 7 C) is dangerously close to the pH below which there is rapid deterioration of function. On the other hand, perfusate pHs up to 7.75 in dogs and 8.25 in rabbits were tolerated at no detriment. As a result, the recommendation is made to carry out hypothermic organ perfusion at a pH well above 7.4; 7.60 or 7.65 seems reasonable.

Distribution of ventilation in the turtle Pseudemys scripta.

Spontaneously ventilating turtles, Pseudemys scripta, were allowed to rebreathe 133Xe to equilibrium. Frequent gamma camera images were obtained and processed to allow regional evaluation of ventilation. The distribution of ventilation was markedly inhomogeneous, with washin to equilibrium most rapid in anterior lung compartments and slowest in posterior lung compartments. Similarly washout from equilibrium was most rapid in anterior compartments and slowest in posterior compartments. During apnea intercompartmental gas exchange occurred rapidly during spontaneous activity of the limbs or, more slowly, during episodes ascribed to regional contraction of lung smooth muscle. Despite inhomogeneous ventilation, overall washout of 133Xe could be monoexponential. A simple series model of the turtle lung is consistent with the inhomogeneous ventilation observed.

The effects of temperature on acid-base balance and ventilation of the marine iguana.

Marine iguanas, Amblyrhynchus cristatus, held for 12-18 h at 16, 24 and 35 degrees C exhibited an arterial pH change of -0.001 delta pH/delta degree C. The arterial pH changed by -0.004 delta pH/delta degree C between 16 and 24 degrees C and by -0.015 delta pH/delta degree C between 24 and 35 degrees C. When the animals were allowed to cool to 16 degrees C and remarm to 35 degrees C after 12-18 h at 35 degrees C, the pH change was -0.015 delta pH/delta degree C. Arterial pH measured during warming to 35 degrees C after 12-18 h at 16 degrees C was relatively constant at around pH approximately equal to 7.60 returning slowly toward the 35 degrees C equilibrijm pH approximately equal to 7.44. An increase in VE/MCO2 (L . mmol-1) is seen with decline in equilibrium body temperature from 0.79 at 35 degrees C to 1.66 at 16 degrees C. The ventilatory response is associated with a fall in PaCO2 (24 Torr, 35 degrees C; Torr, 16 degrees C). Arterial CO2 content and [HCO3-] remain relatively constant. The observed arterial pH-body temperature relationshi is similar to other reptiles; however, thermal history appears to influence the relationship. Marine iguanas probably experience only brief periods of time at body temperature as low as 18 degrees C.

Cardiorespiratory effects of temperature in the turtle, Pseudemys floridana.

Weight specific VO2 of resting Pseudemys floridana at body temperatures (BT) between 12 to 38 C was studied in relationship to VE, VT, f, pulmonary and systemic blood flow, and blood PO2, PCO2, pH and O2 content. The slope of the curve for VO2 against body mass was similar to that for mammals and differed from that of lizards. VE increased with BT while VE/VO2 fell, resulting in an elevation of arterial PCO2 and a decline in arterial pH of 0.013 unit/degrees C [HCO-3] and total CO2 remained constant. Increments in VE were achieved by decreasing apneic time and increasing VT up to VT of 18 ml.kg-1 when further rise in VE was exclusively on account of breathing frequency. Mean pulmonary and arterial blood flows were incremented in direct proportion to VO2, and no net intracardiac shunts was demonstrable. Ventilation-perfusion ratio fell with BT while EO2 increased. Arterial hemoglobin saturation varied inversely with BT while the arteriovenous O2 difference remained constant. EO2 was found to be highly dependent on the constant blood convection requirement as VE/VO2 fell. At similar BT, VE/VO2 was similar to that for man while Qpul/VO2 was in inverse proportion to maximum O2 capacity of the blood for the two species.

Oxidative cost to ventilation in a turtle, Pseudemys floridana.

Estimates of oxidative cost of ventilation for Pseudemys floridana were obtained by comparison of mean resting VO2 with that obtained while artificially ventilating the lungs with a constant air flow in excess of the normal VE, a circumstance during which the animals remained apneic due to reduction in alveolar PCO2. At a body temperature of 22 degrees C, the oxidative cost attributable to ventilation was 0.0047 ml O2/ml gas ventilated, a value about 10 times that of man. This cost of ventilation is then related to values of VO2 and VE at various body temperatures. The oxidative cost of ventilation, expressed as a percentage of resting VO2, is given by the equation: cost = 0.47 VE/VO2. Relative cost declines with body temperature since VE/VO2 (resting) declines according to the equation: VE(BTPS)/VO2 = -0.017 BT -0.025 log Wt + 2.01 where units are in ml, kg and min. At body temperatures of 10 and 37 C relative costs were 30 and 10% VO2, respectively. While the inverse relation between VE/VO2 and body temperature has important implications for regulation of arterial pH through influencing arterial PCO2, it has the additional meaning of reducing the relative oxidative cost of ventilation as VO2 increases.

Unilateral renovascular hypertension in rats. Measurements of medullary granules, juxtaglomerular granularity and cellularity, and areas of adrenal zones.

To produce hypertension, the left renal artery was clipped in 20 rats. Six rats had a sham operation. After 4 months, some of the rats showed only a moderate increase in blood pressure, and a second clipping of the same artery was performed. When hypertension became severe in some of the rats, 2 to 4 weeks later, all rats were sacrificed. The "clipped" rats were divided into four groups depending on whether they had little change in blood pressure, acute hypertension, chronic hypertension, or chronic and superimposed acute hypertension. The average adrenal weights were increased in the two groups with acute hypertension. The area of the adrenal glomerular zone was increased in all three groups with hypertension. The groups with acute hypertension also showed increases in the combined areas of (1) the medullary and androgenic zones and possibly (2) the fascicular and reticular zones. The granules of the left juxtaglomerular apparatus were greatly increased in the group with acute hypertension, but were only slightly elevated in the group with chronic hypertension and the group with chronic and superimposed acute hypertension. An increased juxtaglomerular cellularity in the clipped kidney correlated best with hypertension. Renal medullary granular counts were decreased in the right and left kidneys of all clipped groups whether or not they had hypertension, but no changes were found in the amount of medullary interstitial space. The above results are consistent with the evidence in acute unilateral renovascular hypertension with the opposite kidney intact that the clipped kidney is responsible initially via a renin-angiotensin-aldosterone mechanism, with participation by the major adrenal zones. In chronic hypertension some other mechanisms, with participation by the major adrenal zones. In chronic hypertension some other mechanisms, which seem to be related to juxtaglomerular cellularity in the clipped kidney, are operating. Other evidence suggests that such mechanisms may depend on sodium retention, volume expansion, and increased sensitivity to vasoconstrictors.