Effects of head and body cooling on hemodynamics during immersed prone exercise at 1 ATA

Immersion pulmonary edema (IPE) is a condition with sudden onset in divers and swimmers suspected to be due to pulmonary arterial or venous hypertension induced by exercise in cold water, although it does occur even with adequate thermal protection. We tested the hypothesis that cold head immersion could facilitate IPE via a reflex rise in pulmonary vascular pressure due solely to cooling of the head. Ten volunteers were instrumented with ECG and radial and pulmonary artery catheters and studied at 1 atm absolute (ATA) during dry and immersed rest and exercise in thermoneutral (29-31 degrees C) and cold (18-20 degrees C) water. A head tent varied the temperature of the water surrounding the head independently of the trunk and limbs. Heart rate, Fick cardiac output (CO), mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), pulmonary artery wedge pressure (PAWP), and central venous pressure (CVP) were measured. MPAP, PAWP, and CO were significantly higher in cold pool water (P < or = 0.004). Resting MPAP and PAWP values (means +/- SD) were 20 +/- 2.9/13 +/- 3.9 (cold body/cold head), 21 +/- 3.1/14 +/- 5.2 (cold/warm), 14 +/- 1.5/10 +/- 2.2 (warm/warm), and 15 +/- 1.6/10 +/- 2.6 mmHg (warm/cold). Exercise values were higher; cold body immersion augmented the rise in MPAP during exercise. MAP increased during immersion, especially in cold water (P < 0.0001). Except for a transient additive effect on MAP and MPAP during rapid head cooling, cold water on the head had no effect on vascular pressures. The results support a hemodynamic cause for IPE mediated in part by cooling of the trunk and extremities. This does not support the use of increased head insulation to prevent IPE.

Plasma glucose response to recreational diving in novice teenage divers with insulin-requiring diabetes mellitus

A growing number of individuals with insulin-requiring diabetes mellitus (IRDM) dive, but data on plasma glucose (PG) response to diving are limited, particularly for adolescents. We report on seven 16-17 year old novice divers with IRDM participating in a tropical diving camp who had recent at least moderate PG control (HbA1c 7.3 +/- 1.1%) (mean +/- SD). PG was measured at 60, 30 and 10 min pre-dive and immediately following 42 dives. Maximum depth (17 +/- 6 msw) and total underwater times (44 +/- 14 min) were not extreme. Pre-dive PG exceeded 16.7 mmol x L(-1) (300 mg x dL(-1)) in 22% of dives. Males had significantly higher pre-dive levels (15.4 +/- 5.6 mmol x L(-1) [277 +/- 100 mg x dL(-1)] vs. 12.8 +/- 2.9 mmol x L(-1) [230 +/- 52 mg x dL(-1)], respectively) and greater pre-post-dive changes (-4.3 +/- 4.4 mmol x L(-1) [-78 +/- 79 mg x dL(-1)] vs. -0.5 +/- 4.3 mmol x L(-1) [-9 +/- 77 mg x dL(-1)], respectively). Post-dive PG was < 4.4 mmol x L(-1) [< 80 mg x dL(-1)] in two dives by two different males (3.4 and 3.9 mmol x L(-1) [61 and 70 mg x dL(-1)]). No symptoms or complications of hypoglycemia were reported. These data show that in a closely monitored situation, and with benign diving conditions, some diabetic adolescents with good control and no secondary complications may be able to dive safely. The impact of purposeful elevation of PG to protect against hypoglycemia during diving remains to be determined.

Plasma glucose responses in recreational divers with insulin-requiring diabetes

Insulin-requiring diabetes mellitus (IRDM) is commonly described as an absolute contraindication to scuba diving. A 1993 Divers Alert Network survey, however, identified many active IRDM divers. We report on the plasma glucose response to recreational diving in IRDM divers. Plasma glucose values were collected before and after diving in IRDM and healthy control divers. Time/depth profiles of 555 dives in IRDM divers were recorded. IRDM divers had been diving for a mean of almost nine years and had diabetes for a mean of over 15 years. No symptoms or complications related to hypoglycemia were reported (or observed). Post-dive plasma glucose fell below 70 mg x dL(-1) in 7% (37/555) of the IRDM group dives compared to 1% (6/504) of the controls (p<0.05). Moderate levels of hyperglycemia were also noted in 23 divers with IRDM on 84 occasions. While large plasma glucose swings from pre-dive to post-dive were noted, our observations indicate that plasma glucose levels, in moderately-controlled IRDM, can be managed to avoid hypoglycemia during routine recreational dives under ordinary environmental conditions and low risk decompression profiles.

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.