SUMMARY1. Heat acclimation was induced in eight subjects by asking them to exercise until exhaustion at 60 % of maximum oxygen consumption rate (VO ) for 9-12 consecutive days at an ambient temperature of 40°C, with 10% relative humidity (RH). Five control subjects exercised similarly in a cool environment, 20 0C, for 90 min for 9-12 days; of these, three were exposed to exercise at 40°C on the first and last day.2. Acclimation had occurred as seen by the increased average endurance from 48 min to 80 min, the lower rate of rise in the heart rate (HR) and core temperature and the increased sweating.3. Cardiac output increased significantly from the first to the final heat exposure from 19 6 to 21V4 1 min-1; this was possibly due to an increased plasma volumne and stroke volume. 4. The mechanism for the increased plasma volume may be an isosmotic volume expansion caused by influx of protein to the vascular compartment, and a sodium retention induced by a significant increase in aldosterone.5. The exhaustion coincided with, or was elicited when, core temperature reached 39-7 + 0 15°C; with progressing acclimation processes it took progressively longer to reach this level. However, at this point we found no reduction in cardiac output, muscle (leg) blood flow, no changes in substrate utilization or availability, and no recognized accumulated 'fatigue' substances.6. It is concluded that the high core temperature per se, and not circulatory failure, is the critical factor for the exhaustion during exercise in heat stress.

SUMMARYRegional myocardial blood flow has been thought to be relatively uniform, in accord with the singular function of myocardial cells. However, considerable spatial heterogeneity has been observed in the hearts of anesthetized animals and in isolated hearts. Studies were undertaken in a total of 13 baboons. Eleven were awake, healthy animals sitting in chairs at rest or feeding, some performed mild leg exercise (wheel turning), and others were subjected to whole body heating; two were anesthetized, methodological controls. Microspheres (15 ± 3 μm diameter, 0.5 × 10 6 /kg body weight) were injected via a catheter into the apex of the left ventricle while arterial blood was sampled at a constant rate for calculating cardiac output. Microspheres with different labels were injected at six intervals of 20 minutes to several hours. On sacrifice, the hearts were sectioned into 204 locatable pieces (left ventricle, 168; right ventricle, 27; and atria, 9). Average resting myocardial flow was 2.1 ± 0.2 ml/g per min (mean ± SD, n = 11). Left and right ventricles and atria comprised 70 ± 2% (n = 13), 20 ± 2%, and 10 ± 2% respectively of the total heart mass while receiving 80 ± 3%, 16 ± 2%, and 4 ± 2% of the total myocardial flow. Thus, mean left ventricular flow was 114 ± 5% of the average for the whole heart, right ventricular flow was 81 ± 13%, and atrial flow was 41 ± 13%. Myocardial flow heterogeneity was marked; in left ventricle, regional flows ranged from one-third to two times the mean, the relative dispersion (= standard deviation/mean) of regional flows, corrected for methodological scatter and temporal variation, was 0.33 ± 0.06 (n = 67) in the whole heart, 0.26 ± 0.07 in left ventricle, 0.32 ± 0.11 in right ventricle, and 0.22 ± 0.19 in the atria. The pattern of regional flows in each heart tended to remain stable with time. In each piece averaged over time, the relative dispersion due to temporal heterogeneity was 0.11 ± 0.03 (n = 2040) in the whole heart, 0.09 ± 0.03 in the left ventricle, 0.15 ± 0.05 in the right ventricle, and 0.23 ± 0.06 in the atria. The conclusion is that the degree of spatial heterogeneity of local myocardial flows in conscious primates is similar to that of anesthetized animals and isolated hearts, and is much greater than that due to temporal fluctuations. KeywordsFlow distribution; Coronary arteries; Septal perfusion; Tracer-labeled microspheres; Awake primates; Spatial variation in flow; Temporal variation in flowWith the increasing refinement of biochemical and physiological observations, the variations that occur throughout the myocardium in rates of metabolism (Griggs et al., 1972) We appreciate the help of G. Crookcr in the preparation of the manuscript, and of H. Nurk with the illustrations. Presented in part at FASEB, Fed. P.roc. 37: 875, 1978. NIH Public Access (Gamble et al., 1974;Schubert et al., 1978;Weiss and Sinha, 1978), and in flow (Domenech et al., 1969;Yipintsoi et al., 1973) have become quite evident. It is no longer sufficient either in concept or in practi...

The aim of this study was to investigate the effects of individual physical characteristics on preweaning survival and growth of piglets born in a noncrate system. Data were collected from 3,402 neonatal piglets from 203 Landrace × Yorkshire sows housed in noncrate pens in a commercial Danish sow herd. Piglets were categorized into groups according to their survivability: surviving to weaning (SURV), stillborn (STILL), or dead between birth and weaning (DBW), which was subdivided into dead d 0 to 1 after farrowing (DEAD1) or dead d 2 to 26 after farrowing (DEAD26). Linear models were used to determine which physical characteristics affected survivability and growth of piglets. Results showed that characteristics related to the individual piglets had a greater degree of explanatory power in relation to survival than variables related to the sow. Survival of piglets increased if piglets were females (P < 0.001), had a greater body mass index (P < 0.001), and were born to sows of parity 3 or more (P = 0.017). Piglets with a greater birth weight were more likely to survive (P < 0.001), but birth weight was inferior to body mass index in explaining differences between SURV and DBW. Piglets that died 2 to 26 d after birth had a lower birth weight (P < 0.001), were born to sows of parity 1 or 2 (P = 0.014), and were born after a shorter gestation (P = 0.011) compared with SURV. Piglets that died on d 0 to 1 after birth had a lower body mass index (P < 0.001), displayed a greater degree of growth restriction (P = 0.004), and were born in large litters (P = 0.005). The gender of the piglets affected survivability at both d 0 to 1 (P < 0.001) and d 2 to 26 (P < 0.001). Piglets in DEAD1 differed from STILL by having a shorter crown to rump length (P < 0.001), a birth weight that deviated more from the mean weight of the litter (P = 0.001), and being more likely to be born before d 116 of gestation (P = 0.008). The only physical characteristic that was important for growth performance in the suckling period was birth weight (P < 0.001), yet using only birth weight as an indicator for survivability was too simplistic. The results of this study emphasize that individual characteristics of neonatal piglets could serve as indicators of survivability of piglets born in noncrate systems; however, the results suggest that the importance of characteristics differed in different periods of the preweaning period.

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