Arterial blood gases during diving in elite apnea divers

Elite apnea divers have considerably extended the limits of dive depth and duration but the mechanisms allowing humans to tolerate the compression- and decompression-induced changes in alveolar gas partial pressures are still not fully understood. Therefore we measured arterial blood gas tensions and acid-base-status in two elite apnea divers during simulated wet dives lasting 3 : 55 and 5 : 05 minutes, respectively. Arterial pO2 followed the compression-(from 13.8/16.9 kPa before the dive to 30 kPa at the start of the bottom time) and decompression-induced (from 13.7/21.0 kPa to 3.3/4.9 kPa immediately after surfacing) variations of ambient pressure, while the arterial pCO2 remained within the physiologic range (3.0/3.9 kPa before diving vs. 5.7/5.9 kPa at the end of the bottom time), probably due to the CO2 storage capacity of the blood. These findings may help to explain why humans can sustain deep and long apnea dives without major increases in respiratory drive.     

The relative risk of decompression sickness during and after air travel following diving

BACKGROUND: Decompression sickness (DCS) can be provoked by post-dive flying but few data exist to quantify the risk of different post-dive, preflight surface intervals (PFSI). METHODS: We conducted a case-control study using field data from the Divers Alert Network to evaluate the relative risk of DCS from flying after diving. The PFSI and the maximum depths on the last day of diving (MDLD) were analyzed from 627 recreational dive profiles. The data were divided into quartiles based on surface interval and depth. Injured divers (cases) and uninjured divers (controls) were compared using logistic regression to determine the association of DCS with time and depth while controlling for diver and dive profiles characteristics. These included PFSI, MDLD, gender, height, weight, age, and days of diving. RESULTS: The means (+/-SD) for cases and controls were as follows: PFSI, 20.7 +/- 9.6 h vs. 27.1 +/- 6.7 h; MDLD, 22.5 +/- 14 meters sea water (msw) vs. 19 +/- 11.3 msw; male gender, 60% vs. 70%; weight, 75.8 +/- 18 kg vs. 77.6 +/- 16 kg; height, 173 +/- 16 cm vs. 177 +/- 9 cm; age, 36.8 +/- 10 yr vs. 42.9 +/- 11 yr; diving > or = 3 d, 58% vs. 97%. Relative to flying > 28 h after diving, the odds of DCS (95% CI) were: 1.02 (0.61, 1.7) 24-28 h; 1.84 (1.0, 3.3) 20-24 h; and 8.5 (3.85, 18.9) < 20 h. Relative to a depth of < 14.7 msw, the odds of DCS (95% CI) were: 1.2 (0.6, 1.7) 14.7-18.5 msw; 2.9 (1.65, 5.3) 18.5-26 msw; and 5.5 (2.96, 1 0.0) > 26 msw. CONCLUSIONS: Odds ratios approximate relative risk in rare diseases such as DCS. This study demonstrated an increase in relative risk from flying after diving following shorter PFSIs and/or greater dive depths on the last day. The relative risk increases geometrically as the PFSI becomes smaller.     

Desbaric air embolism during diving: an unusual complication of Osler-Weber-Rendu disease

Cerebral manifestations of Osler-Weber-Rendu disease (OWRD, hereditary haemorrhagic telangiectasia) including telangiectases, venous malformations, and arteriovenous malformations, are usually under-recognised. The highest complication rate is observed in high flow cerebral arteriovenous malformations, which may present with headache, epilepsy, ischaemia, or haemorrhage. Cerebral air embolism during self-contained underwater breathing apparatus (scuba) diving as the first manifestation of pulmonary arteriovenous malformation (PAVM) in OWRD patients has never been reported before. Here we report a 31 year old male who presented desbaric air embolism as the first manifestation of PAVM. As far as we know, this is the first such case published in English medical literature.     

Peripheral and central blood flow in man during cold, thermoneutral, and hot water immersion.

Cardiovascular reflexes were studied during immersion in water to the chest. Cardiac output (CO) was determined by acetylene rebreathing; forearm muscle and subcutaneous blood flow by 133Xe-clearance; and cutaneous blood flow by laser Doppler. Measurements were taken in a) control situation (CTR) (subject sitting dry); b) immersed in thermoneutral (NWI); c) in cold (CWI); and d) in hot water (HWI). The overall trend was that water immersion per se increased stroke volume (SV), but mostly during NWI and CWI, where heart rate (HR) was decreased by 15%; during HWI, HR increased by 32%, the temperature effect evidently overriding the immersion effect. Insignificant increases in CO were seen in NWI and HWI (18% and 44%), and no effect in CWI. Arterial pressure and total peripheral resistance (TPR) increased significantly in CWI due to an increase in peripheral vascular resistance, while significant decreases in TPR and CPR were observed in HWI and tendencies to decreases were found in NWI.     

Measurement of hepatic blood flow with diethyl-ida in man

Hepatic blood flow was estimated by the method based on the hepatic clearance. The substances removed by hepatocytes were indocyanine green and ^99mTc-diethyl-Ida. Hepatic blood flow was estimated in 3 normal patients and 14 patients with cirrhosis. The mean values of hepatic blood flow did not significantly differ when calculated with indocyanine green or with diethyl-Ida: 1,504±491 ml/min (mean±SD) and 1,562±525 ml/min, respectively (P>0.70). The relatively high extraction of diethyl-Ida in patients with cirrhosis suggests that this substance could be used in patients with reduced liver uptake rate.     

40 m模拟空气反复潜水对人血常规的影响

目的 探讨40m模拟空气反复潜水对人血常规的影响。方法16名健康成年男性，连续3d进行6次40m-35min空气模拟潜水。其中8人在3d高气压暴露中服用三联抗氧化剂（维生素C1g／d、维生素E2．5g／d、N-乙酰半胱氨酸8g／d）。分别于暴露前1d和暴露第1天、第2天、第3天下午出舱后抽血行血常规检查。结果模拟潜水后白细胞及其分类、红细胞、血红蛋白、血细胞压积呈上升趋势。白细胞在第1天暴露后与暴露前比差异有统计学意义（P〈0．05）；单核细胞、红细胞、血红蛋白以及血细胞比容在第2、3天暴露后与暴露前相比差异有统计学意义（P〈0．05）。而血小板、平均红细胞容积等指标暴露前后无明显变化。与正常暴露组相比，口服抗氧化剂对各指标没有显著影响。结论 3d6次40m模拟空气潜水对血常规某些指标有一定影响，但均在正常范围内。     

Effects of fractionated radiotherapy on bone blood flow in man

Effects of fractionated irradiation on bone blood flow during and some months after the radiotherapy were measured with a 133Xe washout method from the greater trochanteric regions of human femurs. The results suggest that at low dose levels (CRE from 250 to 1050 reu) the decrease in bone blood flow is small. However, there seems to be a significant decrease in blood flow (about 50%) several months after the irradiation.     

Effect of exercise on portal vein blood flow in man

PURPOSE: Doppler pulsed flow and electronic scanning allow for instantaneous measurement of portal vein flow. This method was used to monitor alterations in splanchnic blood flow during exercise. METHODS: Measurements of portal vein blood flow were performed in eight healthy males at rest and at 10-min intervals during cycle ergometry at 70% of maximal aerobic capacity. Subjects stopped cycling briefly (approximately 30 s) and stopped breathing while measurements were made. Flow was calculated from values obtained for velocity of red blood cell passage and cross-sectional area of the vessel. RESULTS: Cross-sectional area decreased during exercise, resulting in a significant decrease in flow over time (P = 0.0001 by ANOVA). The flow within the portal vein had decreased by 80% after 60 min of exercise (absolute flow, 0.63 +/- 0.13 L x min(-1) at rest and 0.13 +/- 0.04 L x min(-1) at 60 min). CONCLUSION: Electronic Doppler flow measurement of portal vein flow is a viable, noninvasive technique that can be used to measure splanchnic blood flow. Values obtained as a result of intensive exercise are in line with earlier results obtained with other techniques.     

Pulmonary edema following closed-circuit oxygen diving and strenuous swimming

Acute pulmonary edema may be induced by diving and strenuous swimming. We report the case of a diver using closed-circuit, scuba equipment who developed acute dyspnea, hemoptysis, and hypoxemia following a dive in 18 degreesC (64.4 degrees F) water and physical exertion during the swim back to shore. With the growing popularity of recreational scuba diving, emergency physicians are liable to be faced with increasing numbers of diving-related medical problems. Diving-induced pulmonary edema should be included in the differential diagnosis of acute hypoxemia, sometimes accompanied by acid-base abnormalities, when this is seen in a diver.     

Heterogeneous intrahepatic distribution of blood flow in humans

Color-functional imaging of intrahepatic blood flow was developed using the ¹³³Xe clearance method and a gamma camera with a computer system. During the 2 min after intrasplenic injection of ¹³³Xe in saline solution, 24 sequential gamma images were obtained. After setting the hepatic region, ¹³³Xe clearance curves were extracted from the serial images every 6x6 mm element and regional blood flow for each element was calculated. The calculated regional hepatic blood flow values were displayed as color images in eight color steps. Eleven patients with and without liver diseases were studied. In all the patients studied, heterogeneous intrahepatic distribution of blood flow was clearly demonstrated by the functional image of regional hepatic blood flow. Although a consistent pattern of intrahepatic distribution of blood flow was not obtained, greater-flow regions were frequently observed in the right lobe. Repeat studies in two patients demonstrated that the intrahepatic distribution of blood flow varied. The 10–15 s scintiphotosplenoportograms also showed the existence of restricted or preferential intrahepatic distribution of splenic flow. These results strongly suggest that intrahepatic distribution of blood flow in the human liver is heterogenous and variable.     

Effect of antiorthostatic bed rest on hepatic blood flow in man

Physiological changes that occur during exposure to weightlessness may induce alterations in blood flow to the liver. Estimation of hepatic blood flow (HBF) using ground-based weightlessness simulation models may provide insight into functional changes of the liver in crewmembers during flight. In the present study HBF, indirectly estimated by indocyanine green (ICG) clearance, is compared in 10 subjects during the normal ambulatory condition and antiorthostatic (-6 degrees) bed rest. Plasma clearance of ICG was determined following intravenous administration of a 0.5-mg.kg-1 dose of ICG to each subject on two separate occasions, once after being seated for 1 h and once after 24 h of head-down bed rest. After 24 h of head-down bed rest, hepatic blood flow did not change significantly from the respective control value.     

Pulmonary artery pressure increases during commercial air travel in healthy passengers

BACKGROUND: It is not known whether the mild hypoxia experienced by passengers during commercial air travel triggers hypoxic pulmonary vasoconstriction and increases pulmonary artery pressure in flight. Insidious pulmonary hypertensive responses could endanger susceptible passengers who have cardiopulmonary disease or increased hypoxic pulmonary vascular sensitivity. Understanding these effects may improve pre-flight assessment of fitness-to-fly and reduce in-flight morbidity and mortality. Methods: Eight healthy volunteers were studied during a scheduled commercial airline flight from London, UK, to Denver, CO. The aircraft was a Boeing 777 and the duration of the flight was 9 h. Systolic pulmonary artery pressure (sPAP) was assessed by portable Doppler echocardiography during the flight and over the following week in Denver, where the altitude (5280 ft/1610 m) simulates a commercial airliner environment. Results: Cruising cabin altitude ranged between 5840 and 7170 ft (1780 to 2185 m), and mean arterial oxygen saturation was 95 +/- 0.6% during the flight. Mean sPAP increased significantly in flight by 6 +/- 1 mmHg to 33 +/- 1 mmHg, an increase of approximately 20%. After landing in Denver, sPAP was still 3 +/- 1 mmHg higher than baseline and remained elevated at 30 +/- 1 mmHg for a further 12 h. Conclusions: Pulmonary artery pressure increases during commercial air travel in healthy passengers, raising the possibility that hypoxic pulmonary hypertension could develop in susceptible individuals. A hypoxia altitude simulation test with simultaneous echocardiography ('HAST-echo') may be beneficial in assessing fitness to fly in vulnerable patients.     

准备运动与放松运动对剧烈运动中及运动后颈总动脉血流速度的影响

８名男性大学生参加了下列３组实验：（１）单纯５分钟的剧烈运动（大于９０％ｏｆＶＯ２ｍａｘ）;（２）５分钟的准备运动（５０％ｏｆＶＯ２ｍａｘ）后再进行上述剧烈运动;（３）上述剧烈运动后再进行５分钟的放松运动（５５％ｏｆＶＯ２ｍａｘ）。在上述实验的同时,检测了每位被试者的颈总动脉血流平均速度（平均ＶＣＣＡ）、心率（ｆｃ）、左肱动脉平均血压（Ｐｍ）,并根据血流速度参数计算出反映脑血流阻力的指标———阻抗指数（ＲＩ）。结果显示：在５分钟的剧烈运动中,不论有否准备运动,上述４种参数均明显增加。在准备运动中,平均ＶＣＣＡ和ｆｃ均有所增加,ＲＩ的增加几乎达到了剧烈运动时的水平。剧烈运动后,Ｐｍ和ｆｃ很快恢复,放松运动中这两个指标有所恢复。但是平均ＶＣＣＡ和ＲＩ在放松运动中保持着剧烈运动时的高水平。准备运动中阻抗指数明显增加提示脑血流阻力增加,这可防止由于颈总动脉平均血流速度和心率的增加而引起脑血流的过多增加（尤其是对那些有脑血管缺陷的人）,有利于机体接着进行剧烈的运动。本研究中的放松运动可减缓颈总动脉血流平均速度等几种生理指标在剧烈运动后的恢复速度,使剧烈运动后机体（尤其是心脑血管调节功能差的人）的生理功能逐渐得到恢复,?     

Mechanisms and patterns of blood lactate increase during exercise in man

The close balance between the O2 requirement to perform exercise and the O2 supply was analyzed. A non-uniform capillary PO2 can result in anaerobic metabolism in some muscle fibers despite an apparently adequate mean capillary PO2. The pattern of lactate increase for constant work rates and incremental exercise is described. Lactate increases without an increase in pyruvate at a threshold work rate above which the lactate/pyruvate ratio increases. The latter decreases immediately at the start to recovery. From simultaneous measurements of arterial lactate and pyruvate during exercise and recovery, we conclude that the lactate increase at the lactate threshold is consequent to a change in redox state rather than a mass action effect.