Retinal vessel responses to exercise and hypoxia before and after high altitude acclimatisation

Abstract

SummaryComputerised microdensitometry was used to study diameter changes in 93 arterial and 91 venous vessel sites in the retinas of four mountain climbers before and after spending seven weeks in the Himalaya mountains. The vascular response to short term strenuous exercise was measured at sea level, to acute hypoxia of simulated alti tude of 15,000 ft (4,572 m) at rest, and to strenuous exercise while acutely exposed to the same hypoxic condition. Before the mountain exposure, retinal vessels con stricted during exercise -1.9% (arteries); -3.3% (veins) and dilated in acute hypo xia 9.4% (arteries); 8.1 % (veins). Superimposed exercise on hypoxic dilated arteries reduced the vasodilation (9.4% to 6%). After acclimatisation, the same physical work load at sea level constricted the arteries more (-5.4% vs -1.9%) but did not constrict the veins (0.2% vs -3.3%). Superimposed exercise on hypoxic dilated vessels, excessively dilated both arteries (8.4% vs 6.0%) and veins (13.7% vs 8.4%), compared to changes seen before the mountain sojourn. This study shows that phys ical conditioning and long adaptation to hypoxia, significantly change the vascular response of the retina to physical activity both in normal atmospheric conditions and during hypoxic stress. High altitude retinal hemorrhages (HARH) were present in one climber, and the study may indicate why HARH is seen often in young and phys ical well-trained subjects. RETINAL VESSEL RESPONSES TO EXERCISE 769reflect the autoregulatory ability of the eye to withstand elevated flow caused by changes in the systemic circulation.In the present paper, calibre changes of ret inal arteries and veins were studied in physical exercise at sea level, in acute exposure to hypoxia, and in physical exercise super imposed on already hypoxic dilated vessels. The subjects were exposed to identical test protocol before and after seven weeks of strenuous mountain climbing in the Himalaya mountains. We observed that high altitude acclimatisation significantly altered the acute response of retinal circulation to physical exercise both in a hypoxic environment and at sea level. Subjects and methods SubjectsFour male mountaineers, aged 33 (no.1), 42 (no. 2), 64 (no. 3), and 42 (no. 4) (mean: 45) years, were used in the study. One of the sub jects (no. 2) lived 800 m above sea level, while the rest of the group lived at sea level. The youngest climber had not previously been exposed to high altitude, while the others were experienced mountaineers from several expeditions above 5,000 m. None of these expeditions, however, had taken place within the past three years.General medical and eye examinations were performed, and the subjects were found to be in good health. The blood pressure was measured by auscultation in a sitting position after 10 minutes rest. The systolic pressure averaged 142 ± 9 (SD) mmHg and the dias tolic pressure 80 ± 8 mmHg. The intraocular pressure, measured by applanation tono metry in the sitting position, averaged 12 ±

Preserved Pressure Autoregulation but Disturbed Cyclo-Oxygenase and Nitric Oxide Effects on Retinal Arterioles during Acute Hypoxia in Diabetic Patients without Retinopathy

“…The reduced vasoconstriction during hypoxia was in accordance with results from a study in normal persons [11], but may depend on the degree of hypoxia since a similar response was neither found in a study with a verified lower degree of hypoxia [10] nor in a study where a lower oxygen saturation was intended but in which a <2% contraction of retinal arterioles was achieved, and the accompanying changes in the arterial blood pressure were not monitored [3]. L -NMMA reduced the contraction during exercise in diabetic patients without retinopathy as opposed to a previously reported lack of such an effect in normal persons [10,20].…”

“…Acute hypoxia in turn elicits vasodilatation [3], and it has been shown in vitro that hypoxia-induced relaxation of retinal vessels depends on cyclooxygenase (COX) products and nitric oxide (NO) [4]. Therefore, it is possible that these mechanisms may be involved in the pathophysiology of retinal vascular impairment in diabetic retinopathy.…”

Ophthalmological Effects of High Altitude

“…Computerized microdensitometry, hand-held fundus photography and digital image analysis are among other useful clinical tools to evaluate altitude-induced changes in the retina [84]. Meehan et al [85] measured the width of retinal arteries and veins by digital image analysis with a software program.…”

High Altitude Retinal Hemorrhages–An Update

“…Also, the higher the ascent and the longer the duration at high altitudes, the higher the occurrence of retinal hemorrhages. Further studies have implicated that HARH may be seen more often in young and physically well-trained mountaineersespecially in those who undergo strenuous exercise at high altitudes (Brinchmann-Hansen et al, 1989;Arora et al, 2011)-such as in the report by Willmann et al (2011) where mountaineers rapidly ascended to an altitude of 4559 m.…”