הסכנה לפגיעה שקשורה לאספקת הדם למוח (cerebrovascular accident) היא בעקבות העלייה בלחץ הדם, בפועל אין לזה חשיבות.
חבל שלא עברת על הקישור שתומר שם, אני מעתיק לפה סקירה של הספרות בנושא שביצעו לון קילגור ומארק ריפטו.
The Valsalva Manuver: Risk or Risk Management?
Becky Kudrna, Lon Kilgore, PhD, and Mark Rippetoe
Within the clinical community, the major risk associated with the Valsalva maneuver is cerebrovascular accident. The term cerebrovascular accident can refer to stroke, aneurysm, or hemorrhage of the blood vessels of the brain. It has been suggested that the extremely high, although transient blood pressures created when an individual utilizes the Valsalva maneuver are simply too high for the vessel walls to handle (Linsenbardt et al., 1992). Thus conventional wisdom states that the Valsalva maneuver causes cerebrovascular accidents by raising blood pressure beyond a safe level.
There have been documented cases of cerebrovascular accident occurring while weightlifting. Haykowsky et al. (1996) reported three case studies of subarachnoid hemorrhage in otherwise healthy individuals during weight training. These authors noted that all of the individuals recovered and returned to normal activities within 3 months. Cayen & Cullen, report an additional case of cerebral hemorrhage during resistance exercise in 2002. A fifth occurrence was reported in an anabolic steroid user who suffered both a myocardial infarction and cerebral hemorrhage during resistance exercise, (Kenedy et al., 1993). This individual died as a result of his injuries. In deceased populations, one case of a cerebral hemorrhage occurred in a preexisting brain tumor during resistance exercise, (Goetting & Swanson, 1987). Finally, one case of an effaced lateral ventricle and one case of a subdural hematoma were reported in two males performing sit-ups with the Valsalva maneuver (Uber-Zac & Venkatesh, 2002). It is important to note here that of all the reported cases of CVA in both healthy and diseased populations only one resulted in mortality.
Whereas Narloch & Brandstater (1995) and Uver-Zac & Venkatesh (2002) interpreted the cause of the cerebrovascular hemorrhage in two male recreational lifters as transient vascular hypertension caused by the Valsalva maneuver, Haykowsky et al. (1996), attributed the three cases of subarachnoid hemorrhage in resistance-exercised individuals to preexisting, but undetected aneurysms. Haykowsky (1996), and McCartney (1999) suggest that the few incidences of CVA that do occur with resistance exercise may be linked to undetected cerebral aneurysms and thus are not entirely attributable to resistance exercise or the Valsalva maneuver. According to McCartney, approximately 1% of the population has cerebral aneurysms and the response of such individuals to the transient stresses of weightlifting should not be viewed as the normal or typical response. With millions of people participating in resistance exercise daily, the small number of reported CVA events actually represents a frequency that is statistically insignificant.
When considering exercise induced CVA it is important to understand that aerobic exercise, an exercise modality that is not associated with the Valsalva maneuver is also associated with a small number of CVA incidences, (Cayen & Cullen, 2002).
Not all researchers hold that the Valsalva maneuver during resistance exercise is dangerous. McCartney (1999) and Hughes et al., (1989) acknowledged that the Valsalva maneuver is an instinctive response and should be used particularly in lifts above 85% of 1 repetition maximum. Further, there is compelling evidence suggesting the Valsalva maneuver actually prevents catastrophic cerebrovascular injuries rather than causes them.
The work of Haykowsky et al. (2003) suggests that elevated vascular pressure is only dangerous to the delicate vascular walls of the brain if intracranial pressures remain low, and thus transmural pressure is high. Essentially, if the pressure surrounding the vessel increases and pushes back against the vessel wall, the blood pressure within the vessel will not be transmitted across to the cranial tissue, meaning that transmural pressure is low. The measure of the difference in pressures between vascular pressure and intracranial pressure should therefore be a better indicator of the stress the vessel walls are under and thus be a better indicator of the danger of cerebrovascular accident. Haykowsky et al, (2003) found that performing the Valsalva maneuver decreased the pressure differences across the cerebrovascular wall, theoretically decreasing the risk of aneurysm or hemorrhage. This finding corroborated the much earlier and ignored work of Hamilton et al. (1944). These studies strongly suggest that performing a heavy lift without the Valsalva maneuver places individuals at greater risk of CVA than performing the same lift with the Valsalva maneuver. This is directly contrary to the conventional wisdom.
The mechanism through which the Valsalva maneuver raises intracranial pressure is theorized as follows: (1)The Valsalva maneuver directly increases thoracic pressure by attempting to force air through the closed glottis. (2)This elevated thoracic pressure is transferred to the cerebrospinal fluid in much the same way that thoracic pressure increases abdominal pressure. Because the cerebrospinal fluid surrounding the spinal cord is continuous with fluid of the subdural space in the skull, intracranial pressure also rises. The rapid nature of fluid pressure transfer within this system means that arterial pressure and intracranial pressure rise at the same rate, yielding a balanced transmural pressure from the beginning to the end of the lift. Thus the lifter is protected throughout the entire lift so long as the Valsalva maneuver is performed.
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