Conséquences cardio-vasculaires d'expositions répétées à l ... - SSA

Research article (ASEM 1996R2)
Abstract : 241 words
Text : Page number : 17, words : 2615, Table number : 1, Figure
number : 0
Reference number : 30
ECHOCARDIOGRAPHY IN MILITARY OXYGEN DIVERS
Running head : Heart and oxygen diving Authors :
Alain BOUSSUGES 1,2CA, MD. PhD, Florence RIERA 1, Pascal ROSSI 2, MD. PhD,
Jean-Eric BLATTEAU 3, MD, Olivier CASTAGNA1, MD, François GALLAND1, MD 1 - Naval Medical Institute (IMNSSA), Boulevard de Sainte-Anne, Toulon-
France 2 - Mediterranean University, E.A. 3280, Laboratoire de Physiopathologie et
Action Thérapeutique des Gaz sous Pression, Faculté de Médecine Nord, 13916
Marseille cedex 20, France. 3 - Département de Médecine Hyperbare, HIA Sainte Anne, Toulon Armées
CA : ( Dr Boussuges Alain, IMNSSA, BP 610 - 83800 Toulon Armées, France
Phone : (33-4) 94 09 92 67, Fax : (33-4) 94 09 92 51.
Email : alainboussuges@libertysurf.fr , a.boussuges@imnssa.net
ABSTRACT
Background : Oxygen divers undergo environmental stressors such as
immersion, ventilation through the SCUBA, cold exposure and increased
ambient pressure. All of these stressors may be responsible for acute
hemodynamic modifications. We hypothesised that repeated hyperbaric
hyperoxia exposure induces long term cardio-vascular modifications.
Methods: A Doppler-echocardiography was conducted on 20 oxygen
military divers (average 12 yr diving experience) and compared to 22
controls. Parameters known to be modified by acute hyperoxic exposure such
as left ventricular (LV) function (systolic and diastolic) and arterial
compliance were analyzed.
Results: Controls and divers were matched appropriately for age and
height, although the divers had a higher body mass index and aerobic
capacity. Left atrial and left ventricular diameters did not differ between
the two groups. On the other hand, left ventricular mass was significantly
higher in the elite military divers (209 +/- 43g) in comparison with the
control group (172 +/- 48g), even when LV mass was indexed to body surface
area. Left ventricular systolic and diastolic function indices, stroke
volume, cardiac index, peripheral vascular resistance and systemic
compliance were comparable between the two groups.
Conclusion: A greater LV mass was observed in oxygen military divers.
The echocardiographic differences between divers and controls could be
attributed to the high level physical training undertaken by the military
divers. But some stressors such as cold water immersion, repeated hyperoxic
exposures, SCUBA breathing and long distance swimming could have
participated to the echocardiographic findings in oxygen divers. Words: 241
Key words: Oxygen toxicity, diving, hyperbaria, hemodyamic status,
echocardiography INTRODUCTION During exposure to hyperbaric environments such as diving with self
contained underwater breathing apparatus (SCUBA) or industrial activities,
supplemental oxygen is given to decrease the nitrogen content of the
tissues and blood at the time of the decompression, and therefore limit the
occurrence of decompression sickness. In the particular case of military
divers, the utilisation of breathing gas enriched with oxygen, through a
closed-circuit SCUBA, provides longer self-sufficiency (expired gas is re-
inhaled, after CO2 has been extracted by lime) and enhanced discretion
(absence of bubbles).
During the dive, subjects undergo environmental stressors such as
immersion, ventilation through the SCUBA, cold exposure and increased
ambient pressure. All of these stressors may be responsible for hemodynamic
modifications which have been well studied in healthy volunteers.
Immersion in water induces a cephalad shift of peripheral venous blood
that augments central blood volume (12, 8).
Ventilation against resistance induces modifications of intra-thoracic
pressure and consequently modifications of cardiac preload and after load
(3).
Cerebral and pulmonary oxygen toxicities are well documented and
oxygen diving standards have been established to prevent divers from acute
oxygen toxicity. On the other hand, several hemodynamic modifications can
be induced by acute hyperoxic exposure. Hyperoxia is recognised as a major
factor of heart rate decrease observed at high ambient pressure (10,
27,30). Authors have attributed this heart rate decrease to a
parasympathetic hyperactivity (14,26). A decrease in cardiac output related
to the simultaneous decrease in heart rate and stroke volume is found at
high oxygen partial pressure (1,18,20,30). Furthermore, an increase in
oxygen partial pressure can induce impairment in cardiac relaxation (14).
Finally, systemic vasoconstriction is consistently observed during exposure
to hyperoxia (1,10,24,30).
Although hemodynamic modifications during short-term hyperoxic
exposure or during open sea diving are well documented, little is known
about the long term cardio-vascular consequences of repeated exposures
experienced by oxygen divers.
In a previous study, Stuhr et al (28) have shown that professional
saturation divers have no morphologic or functional cardiologic changes.
However, the hyperoxic exposure of these divers is less than that of oxygen
divers.
We hypothesised that repeated hyperbaric hyperoxia exposure induces
long term cardio-vascular modifications. A Doppler-echocardiographic study
was carried out on a group of elite military oxygen divers and an age-
matched control group to determine if oxygen diving has long term
consequences on cardio-vascular function. MEthods All experimental procedures were conducted in accordance with the
Declaration of Helsinki, and were approved by the ethics committee of the
University of Marseilles (CCPPRB Marseille 1). Each method and the
potential risks were explained to the participants in detail and they gave
written informed consent before the experiment. Subjects reported to the
laboratory in the early afternoon, 2-3 hours after a light meal. All
subjects were non smokers. During the day of the study, they refrained from
consuming coffee or alcohol. They have not dived or exercised for at least
48 hours.
Subjects Twenty trained male military oxygen divers were included in the study.
The subjects were all experienced divers with 500-3000 dives (average 12 yr
diving experience). None of them had experienced decompression sickness in
the past. Their physical activity was assessed by a questionnaire. Body
surface area was calculated according to Dubois Formula: (height in
cm)0.725 x (weight in kg)0.425 x 0.00718. The percentage of body fat and
the fat free mass were obtained from skin fold thickness (13).
Twenty two healthy male controls without regular SCUBA diving activity
were studied. They were subjected to the same examinations as the military
divers. Measurement of maximal oxygen uptake In order to assess individual exercise aptitude, each subject
performed an incremental treadmill test. Gas exchange was assessed using a
breath-by-breath system, which was calibrated before each test. During the
exercise test, subjects breathed through a mouthpiece in order to analyze
expired gas using breath-by-breath rapid response paramagnetic O2 and
infrared CO2 analyzers (Jaeger Oxycon Pro® gas analyser). Exercises were
performed as follows: volunteers started running after reaching a steady-
state gas exchange condition while standing quietly. After a 6 min warm-up
at 8 km/h with an elevation of 2%, speed was increased by 1km/h/min until
exhaustion. VO2 Max was defined as the highest value of oxygen uptake
despite increased workload.
Echographic and Doppler study The ultrasonographic examinations were carried out by an experienced
investigator (AB) using a commercially available Doppler echocardiograph
(Esaote Mylab 30CV,Genova Italy) connected to a 2.5-3.5 MHz transducer
array. Investigations were performed in a quiet room with a stable
environmental temperature (25°C). Subjects remained at rest for 10 min
before the ultrasonographic examination. Heart rate (HR) was recorded by
echocardiogram and the rate was averaged over 60 s. Blood pressure was
measured by a sphygmomanometer on the right arm after each echographic
examination. Pulse pressure (PP) was defined as systolic minus diastolic
blood pressure: PP = SAP - SDP.
Examinations were made using two dimensional and M-mode
echocardiography associated with pulsed and continuous wave Doppler. Images
were obtained via a trans-thoracic approach from the parasternal views
(long axis and short axis) and from an apical four chamber view. The
subjects were placed in a left lateral position for the parasternal views
and in a supine position for the apical four chamber view. Second harmonic
imaging was used to improve the image quality. Doppler recordings were
performed at the end of normal expiration in order to eliminate the effects
of respiration on the parameters studied. Measurements were averaged from
at least three consecutive beats. Tape recordings were obtained at a paper-
speed of 100mm/s with simultaneous tracing of the electrocardiogram.
Examinations were recorded on standard VHS videotape to be reviewed later.
Variables known to be modified by acute hyperoxic exposure such as left
ventricular (LV) function (systolic and diastolic) and arterial compliance
were analyzed. Left atrial diameter (LA), left ventricle end systolic and end
diastolic diameters (LVEDD, LVESD), left ventricle end diastolic
interventricular septal thickness (LVEDSep), left ventricle end diastolic
posterior wall thickness (LVEDPW), right ventricle end diastolic diameter
(RVEDD), and aortic diameter (Ao) were measured by M-mode echocardiography
from the left parasternal short and long axis views (25).
Left ventricular mass (LVM) was assessed by the application of Devereux