Mid Sweden University

Breath-hold diving (freediving) is an underwater sport that is associated with elevated hydrostatic pressure, which has a compressive effect on the lungs that can lead to the development of pulmonary edema. Pulmonary edema reduces oxygen uptake and thereby the recovery from the hypoxia developed during freediving, and increases the risk of hypoxic syncope. We aimed to examine the efficacy of SpO2, via pulse-oximetry, as a tool to detect pulmonary edema by comparing it to lung ultrasound B-line measurements after deep diving. SpO2 and B-lines were collected in 40 freedivers participating in an international deep freediving competition. SpO2 was measured within 17 ± 6 min and lung B-lines using ultrasound within 44 ± 15 min after surfacing. A specific symptoms questionnaire was used during SpO2 measurements. We found a negative correlation between B-line score and minimum SpO2 (rs = −0.491; p = 0.002) and mean SpO2 (rs = −0.335; p = 0.046). B-line scores were positively correlated with depth (rs = 0.408; p = 0.013), confirming that extra-vascular lung water is increased with deeper dives. Compared to dives that were asymptomatic, symptomatic dives had a 27% greater B-line score, and both a lower mean and minimum SpO2 (all p < 0.05). Indeed, a minimum SpO2 ≤ 95% after a deep dive has a positive predictive value of 29% and a negative predictive value of 100% regarding symptoms. We concluded that elevated B-line scores are associated with reduced SpO2 after dives, suggesting that SpO2 via pulse oximetry could be a useful screening tool to detect increased extra-vascular lung water. The practical application is not to diagnose pulmonary edema based on SpO2 – as pulse oximetry is inexact – rather, to utilize it as a tool to determine which divers require further evaluation before returning to deep freediving.

Background: Exposure to cold air is associated with increased morbidity and mortality in the general population. It is difficult to study the effects of whole-body exposure to cold air under controlled conditions in real life. Objectives: The aim of this study was to (1) explore and describe the experience of symptoms in humans during experimental and controlled exposures to cold air, by using controlled environmental chamber exposures and qualitative methodology, and to (2) categorise the symptoms. Method: The study used a randomised, double blind design, in which 34 subjects undertook rest and moderate-intensity exercise in an environmental chamber set to two or three different temperatures (0, −10, and −17°C) on separate occasions. During the chamber exposures, subjects were interviewed. Qualitative content analysis was selected as the method of analysis. Findings: Subjects reported 50 distinct symptoms during the exposures. The symptoms were grouped into ten sub-categories and two major categories; airway versus whole-body symptoms. Conclusion: We have identified a broad range of symptoms in humans undertaking rest and moderate-intensity exercise at sub-zero temperatures. The symptoms and their categories may well be used to more extensively and quantitatively map cold-induced morbidity.

Patrician, Alexander, Harald Engan, David Lundsten, Ludger Grote, Helena Vigetun-Haughey, and Erika Schagatay. The effect of dietary nitrate on nocturnal sleep-disordered breathing and arterial oxygen desaturation at high altitude. High Alt Med Biol 00:000-000, 2017.Sleep-disordered breathing and fluctuations in arterial oxygen saturation (SaO(2)) are common during sleep among lowlanders ascending to high altitude. Dietary nitrate (NO3-) supplementation has been shown to lower the O-2 consumption in various conditions. Our objective was to investigate whether dietary NO3- could reduce sleep-disordered breathing and SaO(2) desaturation during sleep at altitude. Cardiorespiratory responses during sleep were measured in 10 healthy lowlanders at 330m and then again in the Himalayas at 3700-4900m. Each subject received two 70mL shots of either beetroot juice (BR; approximate to 5.0mmol NO3- per shot) or placebo (PL: approximate to 0.003mmol NO3- per shot) in a single-blinded, weighted order over two consecutive nights at altitude. At 2.5-4.5 hours into sleep at altitude, BR increased the SaO(2) desaturation drop (4.2 [0.1]% with PL vs. 5.3 [0.4]% with BR; p=0.024) and decreased the SaO(2) desaturation duration (14.1 [0.9] seconds with PL to 11.1 [0.9] seconds with BR; p=0.0.041). There was a reduction in breaths with flow limitation (p=0.025), but no changes in Apnea-Hypopnea Index (AHI), mean and minimum SaO(2). The study suggests BR supplementation does not improve AHI or oxygenation, but may increase fluctuations in arterial O-2 saturation during sleep at altitude in native lowlanders.

Breath-hold divers train to minimize their oxygen consumption to improve their apneic performance. Dietary nitrate has been shown to reduce the oxygen cost in a variety of situations, and our aim was to study its effect on arterial oxygen saturation (SaO2) after dynamic apnea (DYN) performance. Fourteen healthy male apnea divers (aged 33 ± 11 years) received either 70 mL of concentrated nitrate-rich beetroot juice (BR) or placebo (PL) on different days. At 2.5 h after ingesting the juice, they were asked to perform 2 × 75 m DYN dives in a pool with 4.5-min recovery between dives. Each dive started after 2-min countdown and without any warm-up apneas, hyperventilation, or lung packing. SaO2 and heart rate were measured via pulse oximetry for 90 s before and after each dive. Mean SaO2 nadir values after the dives were 83.4 ± 10.8% with BR and 78.3 ± 11.0% with PL (P < 0.05). At 20-s post-dive, mean SaO2 was 86.3 ± 10.6% with BR and 79.4 ± 10.2% with PL (P < 0.05). In conclusion, BR juice was found to elevate SaO2 after 75-m DYN. These results suggest an oxygen conserving effect of dietary nitrate supplementation, which likely has a positive effect on maximal apnea performance.

INTRODUCTION: Ingesting nitrate-rich beetroot juice (BJ) has been suggested to enhance physical performance by reducing the oxygen cost, which could be useful in apneic diving. We previously found that after ingestion of BJ, arterial oxygen saturation was higher after static apneas (Engan et.al, Resp. Physiol & Neurobiol, 2012) and after dynamic apneas involving exercise (Patrician & Schagatay. Scand.J.Med.Sci.Sports, 2016). Our aim was to investigate the effect of BJ ingestion on spleen contraction and the resulting Hb increase, a mechanism known to prolong apneas (Schagatay et.al, J.Appl.Physiol, 2001).

MATERIALS AND METHODS: Eight volunteers aged 24±2 years simulated diving by performing maximal apneas with face immersion during prone rest ~2.5h after ingesting 70 ml BJ (5 mmol NO3-) or placebo (0.003 mmol NO3-) on separate days in a weighted order. We measured spleen diameters for volume calculation and capillary Hb before and after "dives".

RESULTS: Baseline (mean±SE) spleen volume was 269±33 mL with placebo and 206±27 mL after BJ ingestion (P<0.05). Post "dive" spleen volumes were smaller, but similar at 168±35 mL and 193±25 mL, respectively (NS). Baseline Hb was 145.4±3.4 g/L with placebo and 149.8±2.6 g/L with BJ (P<0.05). Post "dive" Hb had increased to 152.0±4.8 g/L with placebo and 153.7±3.0 g/L with BJ (NS). 

CONCLUSION: With BJ ingestion spleen volume was reduced and Hb elevated even before the "dive". The elevated Hb at the start of apnea would likely have a positive effect on apneic duration by enhancing circulating oxygen stores. The positive effect of nitrate on performance in various sports could in part be due to its spleen-emptying effect, causing a natural blood boosting, which is a novel finding.

Evidence indicates that increases in sympathetic nervous activity (SNA), and acclimatization to high altitude (HA), may reduce endothelial function as assessed by brachial artery flow-mediated dilatation (FMD); however, it is unclear whether such changes in FMD are due to direct vascular constraint, or consequential altered hemodynamics (e.g., shear stress) associated with increased SNA as a consequence of exposure to HA. We hypothesized that 1) at rest, SNA would be elevated and FMD would be reduced at HA compared with sea-level (SL);and 2) at SL and HA, FMD would be reduced when SNA was acutely increased, and elevated when SNA was acutely decreased. Using a novel, randomized experimental design, brachial artery FMD was assessed at SL (344 m) and HA (5,050 m) in 14 participants during mild lower-body negative pressure (LBNP; -10 mmHg) and lower-body positive pressure (LBPP; -10 mmHg). Blood pressure (finger photoplethysmography), heart rate (electrocardiogram), oxygen saturation (pulse oximetry), and brachial artery blood flow and shear rate (Duplex ultrasound) were recorded during LBNP, control, and LBPP trials. Muscle SNA was recorded (via microneurography) in a subset of participants (n = 5). Our findings were 1) at rest, SNA was elevated (P < 0.01), and absolute FMD was reduced (P = 0.024), but relative FMD remained unaltered (P = 0.061), at HA compared with SL; and 2) despite significantly altering SNA with LBNP (+60.3 +/- 25.5%) and LBPP (-37.2 +/- 12.7%) (P < 0.01), FMD was unaltered at SL (P = 0.448) and HA (P = 0.537). These data indicate that acute and mild changes in SNA do not directly influence brachial artery FMD at SL or HA.

Introduction: Dietary nitrate (NO3-) supplementation serves as an exogenous source of nitrite (NO3-) and nitric oxide (NO) through the NO3- NO3- NO pathway, and may improve vascular functions during normoxia. The effects of NO3- supplementation in healthy lowlanders during hypobaric hypoxia are unknown. Purpose: Determine the effect of acute oral NO3- supplementation via beetroot juice (BJ) on endothelial function (flow mediated dilation; FMD) in lowlanders at 3700 m. Methods: FMD was measured using ultrasound and Doppler in the brachial artery of 11 healthy subjects (4 females, age 25 +/- 5 yrs; height 1.8 +/- 0.1 m, weight 72 +/- 10 kg) sojourning to high altitude. In a randomized, double-blinded crossover study design, FMD was measured 3 h after drinking BJ (5.0 mmol NO3-) and placebo (PL; 0.003 mmol No-3(-)) supplementation at 3700 m, with a 24-h wash out period between tests. FMD was also measured without any BJ supplementation pre-trek at 1370 m, after 5 days at 4200 m and upon return to 1370 m after 4 weeks of altitude exposure (above 2500 m). The altitude exposure was interrupted by a decent to lower altitude where subjects spent two nights at 1370 m before returning to altitude again. Results: Ten subjects completed the NO3- supplementation. FMD (mean +/- SD) pre-trek value was 6.53 +/- 2.32% at 1370 m. At 3700 m FMD was reduced to 3.84 +/- 1.31% (p < 0.01) after PL supplementation but was normalized after receiving BJ (5.77 +/- 1.14% (p = 1.00). Eight of the subjects completed the interrupted 4-week altitude stay, and their FMD was lower at 4200 m (FMD 3.04 +/- 2.22%) and at post-altitude exposure to 1370 m (FMD 3.91 +/- 2.58%) compared to pre-trek FMD at 1370 m. Conclusion: Acute dietary NO3- supplementation may abolish altitude-induced reduction in endothelial function, and can serve as a dietary strategy to ensure peripheral vascular function in lowland subjects entering high altitude environments. (C) 2015 Elsevier Inc. All rights reserved.