Effects of exercise during head-down bed rest on postural control.

BACKGROUND: The effects of exercise on postural control during walking were evaluated following exposure to head-down bed rest (BR). METHODS: Two groups of male subjects (N = 18, mean age = 21.4 yr +/- SE 1.0) were exposed to 5 d of 6 degrees head-down bed rest. The experimental group (E) exercised 90 min.d-1 (n = 12 subjects) during the BR while the control group received no intervention (n = 6). The exercise treatment consisted of a combination of isotonic and isokinetic lower extremity exercise training. Electromyographic (EMG) activity in the tibialis anterior, gastrocnemius, vastus lateralis, and biceps femoris was measured during walking before and after BR. RESULTS: Following BR, EMG activity increased in both test subject groups for all muscles (p < 0.05). However, there were no significant differences in EMG activity between the C and E groups either before or after BR. CONCLUSIONS: These data suggest that the ability of the postural control system to adjust to the gravitational environment was compromised as a result of BR. In addition, we conclude that the exercise protocol used was not an effective countermeasure to the alterations in the postural control system.

Adequate crystalloid resuscitation restores but fails to maintain the active hepatocellular function following hemorrhagic shock.

Studies have shown that active hepatocellular function is depressed early after trauma-hemorrhage and persists despite resuscitation with two or three times (x) the volume of maximum bleedout (MB) with lactated Ringer's solution (LR). However, it is not known if a larger volume of fluid resuscitation corrects this dysfunction. To study this, rats were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of the MB volume was returned in the form of LR, and then resuscitated with 4x or 5x the volume of MB with LR. Three doses of indocyanine green (ICG) were given intravenously and [ICG] measured in vivo using an in-vivo hemoreflectometer. The initial velocity of the clearance of ICG was calculated. Maximal velocity of the clearance (Vmax: the number of functional ICG receptors) and kinetic constant (Km: the efficiency of the active transport) were determined from the Lineweaver-Burk plot. Vmax decreased during hemorrhage, was restored to control levels at 0-4 hours after resuscitation, but decreased at 4-8 hours after resuscitation despite restoration of cardiac output following resuscitation with 5x LR. This could be the result of increased TNF release. The Km also decreased during hemorrhage, but increased at 0-1.5 hours and remained at control levels even 4-8 hours after resuscitation. Thus the failure of Vmax to remain at control levels following adequate fluid resuscitation may form the basis of cellular dysfunction and multiple organ failure after severe hemorrhagic shock.

Improved methodology for the evaluation of the velocity of clearance of indocyanine green in the rat.

Velocity of clearance of indocyanine green (ICG) is used for the measurement of liver function. Thirty-nine curves of ICG concentration vs. time, from 24 rats, were evaluated for the best method for the determination of the initial velocity of clearance of ICG. A bolus dose of ICG (0.66 +/- 0.10 mg/kg) was given, and [ICG] was recorded once per second for the 270 seconds from 30 seconds to 5 minutes after ICG administration with the aid of computer-assisted data acquisition. The 39 observed curves were then fit to six equations: a second- and third-order polynomial, the mathematical constant e raised to a first- (first-order kinetics), second-, and third-order polynomial, and an integrated form of the Michaelis-Menten equation. The residual errors of the fitted equation to the observed data were evaluated. First-order kinetics and an integrated form of the Michaelis-Menten equation were the least accurate methods of describing the [ICG]-time curve. The curve was better described by three equations: a third-order polynomial, e raised to a second-order polynomial, and e raised to a third-order polynomial. We recommend that one of the latter three equations be used in the determination of the initial velocity of clearance of ICG.

Measurement of hepatocellular function, cardiac output, effective blood volume, and oxygen saturation in rats.

The available techniques do not permit the measurement of hepatocellular function, cardiac output, effective blood volume, and oxygen saturation in small animals without the need of blood or tissue sampling. We present methodology that permits us to measure the above variables in the rat. Multiple doses of indocyanine green (ICG; 0.16-2.6 mg/kg) were given to pentobarbital-anesthetized rats, and [ICG] was continuously measured by an in vivo hemoreflectometer. Initial velocity of clearance (Vo) was determined from the [ICG] vs. time plot for each dose by nonlinear regression. The maximal velocity of clearance (Vmax; indicating hepatocellular function) was calculated. Vmax was 1) accurately determined using two, three, or four doses of ICG; 2) it was 1.09 +/- 0.16 mg.kg-1.min-1, not different from the Vo of the near-saturating dose of 25 mg/kg; and 3) it decreased after partial hepatectomy. Cardiac output was 41.89 +/- 1.46 ml.100 g-1.min-1, effective blood volume was 6.12 +/- 0.34 ml/100 g, and oxygen saturation was 92 +/- 2%. These methodologies may prove useful in the evaluation of hepatocellular dysfunction and hemodynamic parameters in the rat during and after various diseased states.