The physiological impact of high altitude on nasal and lower airway parameters

Nasal Function Changes at High Altitude

BACKGROUND

An ever-increasing number of people are involved in sport activities at high altitude.

OBJECTIVE

This study aimed to evaluate the pulmonary and nasal functions, including nasal cytology, in healthy volunteers moving for 1 week from an altitude of 2000 m to another of 3400 m.

METHODS

Peak nasal inspiratory flow (PNIF), pulmonary function, including peak expiratory flow (PEF), mucociliary transport time (MCTt), nasal cytology, and oxygen saturation (O₂ sat) were studied in 5 different occasions-T1: at base camp (2000 m); T2: at the mountain refuge (3400 m); T3: after 7 days at 3400 m; T4: after the return at the base camp (2000 m); and T5: at the base camp (2000 m) after 15 days.

RESULTS

With respect to T1, PEF values decreased at T2 (P = .004), T3 (P = .004), T4 (P = .000), and T5 (P = .001). Forced expiratory volume in the first second and forced vital capacity did not differ among the 5 different times of measurements. In regard to T1, PNIF values increased at T2 (P = .003) and T3 (P = .001). MCTt and O₂ sat showed similar but opposite changes with MCTt increased at T2 and T3 in respect to T1 (P = .000 for both), while O₂ sat decreased at T2 and T3 in respect to T1 (P = .000 for both). At nasal cytology, the number of neutrophils increased at T2 in respect to T1 (P = .008). At multivariate analysis, PNIF changed with altitude from T1 to T4 even accounting for the effect of all the other variables (T1 vs T2 PNIF, P = .009; T1 vs T3 PNIF, P = .007; T1 vs T4 PNIF, P = .021).

CONCLUSIONS

Although the study has some limitations, being conducted on a small cohort and at no controlled environmental conditions, data seem to support the utility of MCTt for studying nasal mucosa damage induced by high altitude. Nasal cytology seems to be able to identify the inflammation of the nasal mucosa exposed to hypoxia. Further investigations on larger series and possibly conducted in hypobaric chamber at controlled standardized conditions are necessary in order to confirm these results and, most importantly, the improvement of PNIF at high altitude.

Chronic Exposure to High Altitude: Synaptic, Astroglial and Memory Changes

Long-term operations carried out at high altitude (HA) by military personnel, pilots, and astronauts may trigger health complications. In particular, chronic exposure to high altitude (CEHA) has been associated with deficits in cognitive function. In this study, we found that mice exposed to chronic HA (5000 m for 12 weeks) exhibited deficits in learning and memory associated with hippocampal function and were linked with changes in the expression of synaptic proteins across various regions of the brain. Specifically, we found decreased levels of synaptophysin (SYP) (p < 0.05) and spinophilin (SPH) (p < 0.05) in the olfactory cortex, post synaptic density−95 (PSD-95) (p < 0.05), growth associated protein 43 (GAP43) (p < 0.05), glial fibrillary acidic protein (GFAP) (p < 0.05) in the cerebellum, and SYP (p < 0.05) and PSD-95 (p < 0.05) in the brainstem. Ultrastructural analyses of synaptic density and morphology in the hippocampus did not reveal any differences in CEHA mice compared to SL mice. Our data are novel and suggest that CEHA exposure leads to cognitive impairment in conjunction with neuroanatomically-based molecular changes in synaptic protein levels and astroglial cell marker in a region specific manner. We hypothesize that these new findings are part of highly complex molecular and neuroplasticity mechanisms underlying neuroadaptation response that occurs in brains when chronically exposed to HA.

The effect of high altitude on nasal nitric oxide levels

The aim of the present study was to investigate whether nasal nitric oxide (nNO) levels change in relation to high altitude in a natural setting where the weather conditions were favorable. The present study included 41 healthy volunteers without a history of acute rhinosinusitis within 3 weeks and nasal polyposis. The study group consisted of 31 males (76 %) and 10 females (24 %) and the mean age of the study population was 38 ± 10 years. The volunteers encamped for 2 days in a mountain village at an altitude of 1,500 m above sea level (masl) and proceeded to highlands at an altitude of 2,200 masl throughout the day. The measurements of nNO were done randomly, either first at the mountain village or at sea level. Each participant had nNO values both at sea level and at high altitude at the end of the study. The nNO values of sea level and high altitude were compared to investigate the effect of high altitude on nNO levels. The mean of average nNO measurements at the high altitude was 74.2 ± 41 parts-per-billion (ppb) and the mean of the measurements at sea level was 93.4 ± 45 ppb. The change in nNO depending on the altitude level was statistically significant (p < 0.001). The current investigation showed that nNO levels were decreased at high altitude even if the weather conditions were favorable, such as temperature, humidity, and wind.

The effect of high altitude on olfactory functions

It is known that high-altitude trips cause nasal congestion, impaired nasal mucociliary transport rate, and increased nasal resistance, due to decreased partial oxygen pressure and dry air. It is also known that olfactory perception is affected by barometric pressure and humidity. The aim of the present study was to investigate whether olfactory function changes in relation to high altitude in a natural setting. The present study included 41 volunteers with no history of chronic rhinosinusitis or nasal polyposis. The study group consisted of 31 men (76 %) and 10 women (24 %); the mean age of the study population was 38 ± 10 years. Olfactory testing was conducted using "Sniffin' Sticks" at a high altitude (2,200 ms) and at sea level. Odor test scores for threshold and identification were significantly better at sea level than at high altitude (p < 0.001). The major finding of this investigation was that olfactory functions are decreased at high altitudes.

Peak expiratory flow rate of healthy school children living at high altitude

Background:

Anthropometric and socioeconomic factors are known to influence peak expiratory flow rate, but the effect of altitude has not been established decisively, due to conflicting results of various studies.

Aim:

This study was conducted to evaluate the effect of altitude on peak expiratory flow rate of healthy school children.

Materials and Methods:

A cross-sectional study was conducted in which the peak expiratory flow rate of a group of 290 school children (140 male and 150 female), aged 7-14 years, residing in Shimla (altitude 2150 meters), were compared with the results obtained in an age- and sex-matched control group, consisting of 280 school children (138 male and 142 female), residing in Patiala (altitude 278 meters). Mini Wright Peak Flow Meter was used for the study.

Results:

The mean peak expiratory flow rate value of boys at high altitude (265 ± 92.6 L/min) was significantly higher than those in plain areas (245 ± 82.1 L/min). Similarly, the mean peak expiratory flow rate of highlander girls (250.4 ± 70.2 L/min) was significantly higher than girls of plains (232.6 ± 65 L/min).

Conclusion:

The study suggests that besides anthropometric and socioeconomic factors, altitude is an important determinant of lung function.