Dangerous
06-06-2006, 09:31 AM
Important Bubble Grade Seen in Actual Scuba Diving Conditions CME
News Author: Laurie Barclay, MD
June 2, 2006 — An echocardiographic study done on healthy volunteers in actual scuba diving conditions found an important bubble grade in all, according to a report in the May issue of Chest. The hemodynamic changes suggested that hypovolemia is an important factor and that restoration of fluid balance should be considered after all dives.
"During a scuba dive, subjects undergo environmental constraints such as immersion, exposure to cold, and increased ambient pressure," write Alain Boussuges, MD, PhD, from the Institut de Médecine Navale du Service de Santé des Armées in Marseille, France, and colleagues. "Intravascular gas bubbles are carried from the venous circulation to the pulmonary vessel, where they are eliminated through the lungs. The formation of bubbles is recognized as the basis for decompression illness, but such bubbles are also commonly detected in venous circulation of asymptomatic divers."
In this study, 10 healthy scuba divers dove to a mean depth of 34.3 ± 2.7 m of sea water (113 ± 9 feet). Mean duration of the dive was 25.3 ± 3.5 minutes.
One hour after the dive, microbubbles were detected in the right-heart chambers of all subjects, and left atrial and left ventricular diameters were significantly decreased. Cardiac output measured by aortic blood flow remained unchanged, but heart rate increased and stroke volume decreased after the dive. Left ventricular filling, which was assessed on transmitral profile, was partially increased by atrial contraction. Right cavity diameters were unchanged, but there was an increase of the right ventricular/right atrial gradient pressure.
"The diving profile studied promotes a rather important bubble grade in all volunteers," the authors write. "Two factors can explain these results: low volemia secondary to immersion, and venous gas embolism induced by nitrogen desaturation. Consequently, restoration of the water balance of the body should be considered in the recovery process after diving."
Chest. 2006;129:1337-1343
Learning Objectives for This Educational Activity
Upon completion of this activity, participants will be able to:
* Identify hemodynamic changes associated with scuba diving.
* Specify an intervention that may improve hemodynamic function following recreational scuba diving.
Clinical Context
Summertime implies more outdoor activities, and, for some patients, these activities include scuba diving. Immersion in water and self-contained breathing units are known to produce some interesting effects on the circulation, including a reduction in peripheral blood flow that concentrates blood in the central circulation. This effect, in turn, stimulates increased release of atrial natriuretic peptide and diuresis. In addition, the increase in ambient pressure associated with diving increases the arterial concentrations of oxygen and nitrogen, and the higher levels of oxygen may impair cardiac relaxation.
Previous studies have suggested possible cardiac changes associated with scuba diving. The current study follows up 10 healthy male volunteers with echocardiography before and after diving to document these changes.
Study Highlights
* The 10 men included in the study had an average age of 44 years and a mean body mass index of 25 kg/m2. No participant was taking any medications.
* Study subjects underwent echocardiography at baseline and 1 hour following a 25-minute dive at a mean depth of 34.3 m. Participants breathed a standard mixture of nitrogen and oxygen and wore neoprene diving suits.
* Circulating bubbles following the dive were detected with 2-D echography. Cardiac output was determined from aortic blood flow and heart rate, and left ventricular filling was measured using transmitral blood velocities.
* The main study outcomes were differences in echocardiogram data before and after the experimental dive.
* Baseline echocardiograms were normal in all volunteers. The mean indexed left ventricular mass was 101 g/m2.
* There were no diving complications during the study.
* All participants had evidence of circulating bubbles, and 7 of the 10 divers had grade 3 bubbles (the majority of cardiac periods contained bubble signals singularly or in group).
* Systolic and diastolic blood pressure was not significantly affected by diving. However, heart rate increased by a mean of 9 beats per minute after diving, and stroke volume decreased by a mean of 6 mL. Cardiac output was not significantly changed by diving.
* Left atrial and left ventricular diameters decreased by a mean of 2 to 3 mm after diving.
* There was a relative increase in atrial contraction in left ventricular filling following the dive.
* While right ventricular diameter remained similar before and after diving, the peak velocity of tricuspid regurgitant flow increased after diving.
* The authors conclude that a relative hypovolemia and venous gas embolism help explain the changes in echocardiographic findings following diving, and they recommend oral rehydration following diving. Rehydration might be especially important in the setting of repeated diving.
Pearls for Practice
* Scuba diving can reduce peripheral blood flow, increase the release of atrial natriuretic peptide and diuresis, and increase the arterial partial pressures of oxygen and nitrogen.
* The current study suggests that oral rehydration following recreational scuba diving may reduce echocardiographic changes associated with diving.
News Author: Laurie Barclay, MD
June 2, 2006 — An echocardiographic study done on healthy volunteers in actual scuba diving conditions found an important bubble grade in all, according to a report in the May issue of Chest. The hemodynamic changes suggested that hypovolemia is an important factor and that restoration of fluid balance should be considered after all dives.
"During a scuba dive, subjects undergo environmental constraints such as immersion, exposure to cold, and increased ambient pressure," write Alain Boussuges, MD, PhD, from the Institut de Médecine Navale du Service de Santé des Armées in Marseille, France, and colleagues. "Intravascular gas bubbles are carried from the venous circulation to the pulmonary vessel, where they are eliminated through the lungs. The formation of bubbles is recognized as the basis for decompression illness, but such bubbles are also commonly detected in venous circulation of asymptomatic divers."
In this study, 10 healthy scuba divers dove to a mean depth of 34.3 ± 2.7 m of sea water (113 ± 9 feet). Mean duration of the dive was 25.3 ± 3.5 minutes.
One hour after the dive, microbubbles were detected in the right-heart chambers of all subjects, and left atrial and left ventricular diameters were significantly decreased. Cardiac output measured by aortic blood flow remained unchanged, but heart rate increased and stroke volume decreased after the dive. Left ventricular filling, which was assessed on transmitral profile, was partially increased by atrial contraction. Right cavity diameters were unchanged, but there was an increase of the right ventricular/right atrial gradient pressure.
"The diving profile studied promotes a rather important bubble grade in all volunteers," the authors write. "Two factors can explain these results: low volemia secondary to immersion, and venous gas embolism induced by nitrogen desaturation. Consequently, restoration of the water balance of the body should be considered in the recovery process after diving."
Chest. 2006;129:1337-1343
Learning Objectives for This Educational Activity
Upon completion of this activity, participants will be able to:
* Identify hemodynamic changes associated with scuba diving.
* Specify an intervention that may improve hemodynamic function following recreational scuba diving.
Clinical Context
Summertime implies more outdoor activities, and, for some patients, these activities include scuba diving. Immersion in water and self-contained breathing units are known to produce some interesting effects on the circulation, including a reduction in peripheral blood flow that concentrates blood in the central circulation. This effect, in turn, stimulates increased release of atrial natriuretic peptide and diuresis. In addition, the increase in ambient pressure associated with diving increases the arterial concentrations of oxygen and nitrogen, and the higher levels of oxygen may impair cardiac relaxation.
Previous studies have suggested possible cardiac changes associated with scuba diving. The current study follows up 10 healthy male volunteers with echocardiography before and after diving to document these changes.
Study Highlights
* The 10 men included in the study had an average age of 44 years and a mean body mass index of 25 kg/m2. No participant was taking any medications.
* Study subjects underwent echocardiography at baseline and 1 hour following a 25-minute dive at a mean depth of 34.3 m. Participants breathed a standard mixture of nitrogen and oxygen and wore neoprene diving suits.
* Circulating bubbles following the dive were detected with 2-D echography. Cardiac output was determined from aortic blood flow and heart rate, and left ventricular filling was measured using transmitral blood velocities.
* The main study outcomes were differences in echocardiogram data before and after the experimental dive.
* Baseline echocardiograms were normal in all volunteers. The mean indexed left ventricular mass was 101 g/m2.
* There were no diving complications during the study.
* All participants had evidence of circulating bubbles, and 7 of the 10 divers had grade 3 bubbles (the majority of cardiac periods contained bubble signals singularly or in group).
* Systolic and diastolic blood pressure was not significantly affected by diving. However, heart rate increased by a mean of 9 beats per minute after diving, and stroke volume decreased by a mean of 6 mL. Cardiac output was not significantly changed by diving.
* Left atrial and left ventricular diameters decreased by a mean of 2 to 3 mm after diving.
* There was a relative increase in atrial contraction in left ventricular filling following the dive.
* While right ventricular diameter remained similar before and after diving, the peak velocity of tricuspid regurgitant flow increased after diving.
* The authors conclude that a relative hypovolemia and venous gas embolism help explain the changes in echocardiographic findings following diving, and they recommend oral rehydration following diving. Rehydration might be especially important in the setting of repeated diving.
Pearls for Practice
* Scuba diving can reduce peripheral blood flow, increase the release of atrial natriuretic peptide and diuresis, and increase the arterial partial pressures of oxygen and nitrogen.
* The current study suggests that oral rehydration following recreational scuba diving may reduce echocardiographic changes associated with diving.