3) Effect of bathing
Since physical environment such as temperature change is suspected to be the biggest trigger of bathing accident, let's explore three major effects of bathing; heating effect, water pressure effect and buoyancy effect (Figure 1).
Heating effect induces vasodilatation promoting blood flow to increase oxygen supply to tissues, and it decreases cardiac load as cardiac output increases. However with elderly, heating effect can work the opposite way depending on cardiac function level, and also the effect differs according to dressing room temperature or to water temperature. Blood vessels shrink in cold dressing room and blood tends to gather in heart, brain and organs like digestive ducts. In case of high temperature bathing(about 42°Cand above), blood flow to periphery significantly increases by heating effect right after getting into the tub. With atherosclerotic condition in heart or brain, significant decrease of blood flow can lead ischemia in those organs. Also, longer soaking in high temperature water decreases amount of blood by perspiration and accelerates coagulation of blood that may trigger cerebral or myocardial infarction.
Blood pressure changes significantly during bathing. Blood pressure is already on the rise in a cold dressing room and as soon as soaking in high temperature water it increases even more. Then blood pressure starts to decrease and about 4~5 minutes after soaking systolic blood pressure goes down to 5~30% lower than pre-bathing blood pressure. Blood pressure change is more radical with elderly, hypertension, longer soaking, or when water temperature is higher. In some cases even more blood pressure decrease may happen with the motion standing up as getting out of the tub.
As often seen in elderly, this is suspected to happen with the same mechanism as postprandial hypotension or orthostatic hypotension. The important inducing factors responsible to consciousness disturbance and bathing hot flash that result drowning and drowning down.
In still water, water pressure, which is in proportion to the air pressure and the depth, so called still water pressure (hydrostatic pressure), is in charge. Legs are to bring blood back to the heart and this important role is called 'Leg Pumping'.
Because legs are positioned deeper in the water, venous blood would be flown back to the heart by added still water pressure, and in result cardiac output increases.
However when soaking whole body, by the added still water pressure, the girth of the chest shrinks 1~3cm and the girth of the abdomen shrinks 3~5cm. With the pressured thorax and shrunken girth of the chest, diaphragm is pushed up. And that may result in less blood flow from the heart to the lung and more load to the heart. The heart work is assumed less when soaking only lower body.
The effect of buoyancy to physiological reaction has not been clear. With lightened weight, it's applicable to rehabilitation in the heated pool.
4) 14,000 sudden deaths during bathing a year in Japan
Since the bathroom is a private space, there hardly has been any major research on accidents during bathing. This time with the support of Tokyo Metropolitan Fire Department, based on the result from investigation done from October 1999 to March 2000, cases on sudden death during bathing in Japan were examined. Within 23 districts in Tokyo, there were 628 accidental deaths in 6 months, estimated 866 deaths in a year. With the consideration of age-composition difference in Tokyo and national population, it's calculated to be 14,000 sudden deaths during bathing in Japan in 1999. The number is larger than that of traffic accidents, and in elderly population, is even multiply larger than that of traffic accidents.
Also they were already dead (cardio-pulmonary arrest) at the site in half of the cases. Factors related to sudden death during bathing were analyzed, and as shown in Table 1, more advanced age, female, colder temperature and reported in the early morning are the characteristics that have tendency with mortality. On the other hand, there were fewer deaths in the cases that were occurred in the early evening. Specific information why more deaths during bathing had seen in female haven't been clear, however the relationship between the time of the accident and mortality has an interesting point in terms of human biological rhythm. Vital rhythms such as body temperature and blood pressure have its rhythm in 24-hour period, and it's known that it has the highest value in the late afternoon or in the early evening and the lowest in the early morning.
|
