Regulation of breathing in newborns at high altitude

Resting respiratory parameters and respiratory responses to acute changes in end-tidal O2 and CO2 pressure (PETO2 and PETCO2) were investigated in Peru in 23 newborn and 4 older infants at 3.850 m and in 13 newborns at 800 m. The study was done with the subjects asleep in a thermoneutral environment. The transient increase in ventilation in both high- and low-altitude newborns was followed by a decrease in response to acute hypoxia. During hyperoxia the two groups showed a slight but not clearly significant decrease in ventilation, whereas older high-altitude infants showed a sustained decrease. All subjects showed a prompt and clear response to CO2 inhalation during hyperoxia. We conclude that ventilatory peripheral chemoreflex is not fully developed in newborns regardless of altitude. The weak link in the reflex arc may reside in the afferent component because CO2 response was not impaired. Since hypoxic response became persistent in older infants its blunting in adult high-altitude natives is not a legacy of newborns.     

Control of breathing and adaptation to high altitude in the bar-headed goose

The bar-headed goose flies over the Himalayan mountains on its migratory route between South and Central Asia, reaching altitudes of up to 9,000 m. We compared control of breathing in this species with that of low-altitude waterfowl by exposing birds to step decreases in inspired O(2) under both poikilocapnic and isocapnic conditions. Bar-headed geese breathed substantially more than both greylag geese and pekin ducks during severe environmental (poikilocapnic) hypoxia (5% inspired O(2)). This was entirely due to an enhanced tidal volume response to hypoxia, which would have further improved parabronchial (effective) ventilation. Consequently, O(2) loading into the blood and arterial Po(2) were substantially improved. Because air convection requirements were similar between species at 5% inspired O(2), it was the enhanced tidal volume response (not total ventilation per se) that improved O(2) loading in bar-headed geese. Other observations suggest that bar-headed geese depress metabolism less than low-altitude birds during hypoxia and also may be capable of generating higher inspiratory airflows. There were no differences between species in ventilatory sensitivities to isocapnic hypoxia, the hypoxia-induced changes in blood CO(2) tensions or pH, or hypercapnic ventilatory sensitivities. Overall, our results suggest that evolutionary changes in the respiratory control system of bar-headed geese enhance O(2) loading into the blood and may contribute to this species' exceptional ability to fly high.     

Fertility at low and high altitude in central Nepal

Abstract

Data are reported on ages of menarche, first marriage and first childbirth, migration, venereal disease, birth control, birth spacing and on completed fertility rate in populations of Central Nepal living at low (8,500 feet) and high altitude (12,400 feet). The high‐altitude population reported a significantly lower completed fertility rate which could be partly accounted for by later age at marriage and first childbirth and increased birth spacing. Longer post‐partum ammenorhea and breast feeding did not account for the increased average pregnancy gap.     

Fertility at low and high altitude in Central Nepal

Since the 1930s, a number of different studies have tended to show that fertility is lower at high altitude. The present investigation attempts to provide some answers to this question by examining completed fertility rate (CFR) in Highland and Lowland villages in Central Nepal and relating rate differences to age at menarche, age at 1st childbirth, age at 1st marriage, incidence of venereal disease, birth control (vasectomy or hysterectomy), length of postpartum amenorrhea, and breastfeeding. Data was obtained by direct questioning, and under-reporting of births thus cannot be excluded. Fertility histories were taken from post-menopausal women over the age of 45 years. Results indicate no significant difference in reported menarcheal ages between highlanders and lowlanders. Age at 1st marriage and 1st childbirth were both significantly later in highlanders. CFR was significantly lower in highlanders. It would appear that the reduced fertility rate at high altitude can be partly attributable to later age at marriage and later 1st childbirth. Other factors, e.g., husband absenteeism and remarriage have also been suggested as possible contributors to the observed difference. This paper presents the results of a multiple regression analysis using 9 dependent variables: ages of marriage, 1st childbirth and menarch, the average gap between pregnancies, the average amount of time the husband was away, the number of marriages, presence or absence of venereal disease at some time, whether birth control was practiced and altitude status. Average pregnancy gap, age at 1st childbirth and presence or absence of venereal disease were the only variables that independently made a significcant contribution to CFR variance. The increase in pregnancy gap may be related to longer periods of breastfeeding in high altitude women and there would be a concomitant delay in recommencement of menstruation. In testing the hypothesis, no difference is found in reported duration of breastfeeding or in postpartum amenorrhea. The age at marriage and age at 1st childbirth accounted for over 16% of the explained variance in CFR. Some of the observed difference in CFR can be explained by the difference in marital age but not by the interval between marriage and 1st childbirth, as it was very similar in both groups. The lower CFR among the high altitude population could be due to lowering of biological fecundity at high altitude, or simply a matter of choice. The difference might reflect human reproductive hormone differences between high and low altitude populations. Further research will be needed to determine whether or not differences in CFR can be explained by variation in these factors.     

Blood pressure and heart rate during periodic breathing while asleep at high altitude.

The ventilatory and arterial blood pressure (ABP) responses to isocapnic hypoxia during wakefulness progressively increased in normal subjects staying 4 wk at 5,050 m (Insalaco G, Romano S, Salvaggio A, Braghiroli A, Lanfranchi P, Patruno V, Donner CF, and Bonsignore G; J Appl Physiol 80: 1724-1730, 1996). In the same subjects (n = 5, age 28-34 yr) and expedition, nocturnal polysomnography with ABP and heart rate (HR) recordings were obtained during the 1st and 4th week to study the cardiovascular effects of phasic (i.e., periodic breathing-dependent) vs. tonic (i. e., acclimatization-dependent) hypoxia during sleep. Both ABP and HR fluctuated during non-rapid eye movement sleep periodic breathing. None of the subjects exhibited an ABP increase during the ventilatory phases that correlated with the lowest arterial oxygen saturation of the preceding pauses. Despite attenuation of hypoxemia, ABP and HR behaviors during sleep in the 4th wk were similar to those in the 1st wk. Because ABP during periodic breathing in the ventilatory phase increased similarly to the ABP response to progressive hypoxia during wakefulness, ABP variations during ventilatory phases may reflect ABP responsiveness to peripheral chemoreflex sensitivity rather than the absolute value of hypoxemia, suggesting a major tonic effect of hypoxia on cardiorespiratory control at high altitude.     

Oxygen debt in submaximal and supramaximal exercise in children at high and low altitude

The effect of high altitude (HA) on O2 debt and blood lactate concentration [( L]) was examined in 10- to 13-yr-old children who exhibited the same level of physical fitness. Fifty-one children acclimatized to HA (3,700 m) were compared with 40 children living at low altitude (LA, 330 m) during submaximal (20-95% maximal aerobic power, MAP), maximal and supramaximal (115% MAP) bicycle exercise. Results showed that 1) maximal O2 uptake (VO2max) and maximal heart rate were significantly (P less than 0.001) lower at HA than at LA by 15% and 11 beats X min-1, respectively; 2) for a given absolute work load, O2 debt was higher at HA than at LA, and the slopes of the linear relationships between O2 debt and O2 uptake were significantly higher at HA; 3) when related to percent of VO2max, O2 debts in HA and LA were similar; for 115% MAP maximal O2 debt and [L] were not significantly different (maximal O2 debt, 45.7 +/- 2.7 and 45.9 +/- 3.8 ml X kg-1; [L], 6.0 +/- 0.3 and 6.7 +/- 0.5 mM); and 4) linear relationships between maximal O2 debt and [L] were the same at HA and LA. This suggests that HA did not modify the anaerobic capacity in children.     

Effects of exercise on young and adult cattle at low and high altitude

Nine calves and nine oxen walked on a treadmill in a climatized low pressure chamber for one hour each day, 2 weeks at 400 m and 4 weeks at 3,500 m. The overall effects of walking were: increases in heart rate, pulmonary arterial pressure, rectal temperature, respiratory rate, blood-pH and lactate/pyruvate ratio. Haemoglobin, haematocrit, blood specific gravity and blood viscosity increased in the oxen but decreased in the calves. Blood lactate and blood pyruvate declined in both age groups, plasma viscosity only in the calves. The exercise effects were more pronounced at 3,500 m than at 400 m as exemplified by the following percentile differences (3,500-400 m): in heart rate 26%, mean pulmonary arterial pressure: 22%, respiratory rate: 11%, blood pH: 0.3%, blood lactate: 39%, blood pyruvate: 56%, haemoglobin: 4%, blood viscosity: 5%. Compared with the calves, the oxen experienced larger increases in heart rate and respiratory rate in response to exercise, suggesting a greater rise in metabolic rate: they also showed a more pronounced respiratory alkalosis. Thus, exercise seems to have strained the oxen more than the calves. In the oxen, there was a training effect as judged by reductions in exercising heart rate, respiratory rate and rectal temperature.     

Lung function and breathing pattern in subjects developing high altitude pulmonary edema

Introduction

The purpose of the study was to comprehensively evaluate physiologic changes associated with development of high altitude pulmonary edema (HAPE). We tested whether changes in pulmonary function and breathing pattern would herald clinically overt HAPE at an early stage.

Methods

In 18 mountaineers, spirometry, diffusing capacity, nitrogen washout, nocturnal ventilation and pulse oximetry were recorded at 490 m and during 3 days after rapid ascent to 4559 m. Findings were compared among subjects developing HAPE and those remaining well (controls).

Results

In 8 subjects subsequently developing radiographically documented HAPE at 4559 m, median FVC declined to 82% of low altitude baseline while closing volume increased to 164% of baseline (P<0.05, both instances). In 10 controls, FVC decreased slightly (to 93% baseline, P<0.05) but significantly less than in subjects with HAPE and closing volume remained unchanged. Sniff nasal pressure was reduced in both subjects with and without subsequent HAPE. During nights at 4559 m, mean nocturnal oxygen saturation dropped to lower values while minute ventilation, the number of periodic breathing cycles and heart rate were higher (60%; 8.6 L/min; 97 cycles/h; 94 beats/min, respectively) in subjects subsequently developing HAPE than in controls (73%; 5.1 L/min; 48 cycles/h; 79 beats/min; P<0.05 vs. HAPE, all instances).

Conclusion

The results comprehensively represent the pattern of physiologic alterations that precede overt HAPE. The changes in lung function are consistent with reduced lung compliance and impaired gas exchange. Pronounced nocturnal hypoxemia, ventilatory control instability and sympathetic stimulation are further signs of subsequent overt HAPE.

Registration

ClinicalTrials.gov identifier: {"type":"clinical-trial","attrs":{"text":"NCT00274430","term_id":"NCT00274430"}}NCT00274430     

The lung at high altitude

Men and mammals (excluding the indigenous mountain species) who are born at high altitude, or who ascend to live there for a long period, have to undergo acclimatization which affects virtually every system in the body. Since chronic hypoxia is the most important adverse factor in the mountain environment, the lung plays a major part in the process and shows many alterations in structure and function. However, we remain ignorant about many aspects of acclimatization of the lung to hypoxia especially at the ultrastructural level with respect to those cells whose normal function is not yet established. An account of what is known is given in this paper.     

Hepatic amoebiasis at high altitude

Latent amoebiasis is aggravated at high altitude. Protean manifestations are common. Fever is usually absent. Liver tenderness is not a feature and may have to be specially elicited. Leucocytosis is rare. Bowel symptoms inspite of presence of intestinal ulcerations are usually absent. Response to treatment with emetine or chloroquin is unsatisfactory and relapse rate is high. These points may interest mountaineers and other sojourners to high altitude.     

The athlete at high altitude

Track times at moderate altitudes (7000 to 8000 feet) are modified by decreased wind resistance and by systemic disturbances such as mountain sickness, disruption of training, and a decrease of maximum oxygen intake. The optimum period of acclimatization is probably two to three days. This permits adjustment of cerebrospinal fluid acid-base balance, but minimizes disturbances of plasma volume and stroke volume. Further study is needed to establish whether altitude training can improve performance in sea-level competitions.