Damping control of balance in the medial/lateral direction and the risk of falling in the elderly.

AIMS: A proportional-integral-derivative (PID) control has recently been used as a control algorithm of body balance. The purpose of this study was to elucidate an association of the proportional and derivative gain based on the PID control gain for balance for quiet standing with the risk factor for falls in the elderly. METHODS: The movement of a marker on the back of 23 elderly participants (age 75.6±6.6 years) was measured by our developed device with a complementary metal oxide semiconductor video camera and the trunk sway speed in the medial/lateral (M/L) direction (TSSX) was calculated as absolute values of the whole time series. The PID control gain (proportional gain: K(P), integral gain: K(I), derivative gain: K(D)) was identified using the trunk sway data, and normalized by individual height and weight (K(P)n, K(D)n and K(I)n). Individual risk factor for falls was additionally assessed with the Tinetti Performance Oriented Mobility Assessment (POMA) and the fall risk questionnaire. RESULTS: The score in the POMA and the K(D)n significantly decreased with age (P<0.01). The score in the POMA showed a positive correlation with the K(D)n, and negative correlations with the TSSX and K(P)/K(D) ratios (P<0.01). The average K(D)n and the score in the POMA of fallers were significantly lower than those of non-fallers (P<0.05). CONCLUSION: These results suggest that the decreased damping control by derivative gain for balance in the M/L direction is one of the risk factors for falls in the elderly.

Double inferior vena cava with interiliac vein: a case report and literature review.

The duplication of the inferior vena cava (IVC) is a rare, but well-recognized anomaly. Duplicated IVC has a significant relevance for retroperitoneal surgery and venous interventional radiology. We report a case of duplicated IVC, which was observed during routine dissection of an 84-year-old Japanese female cadaver. The interiliac vein between the duplicated IVC ran obliquely upwards from left to right. We performed systematic literature review of published reports based on Pubmed and Medline from 1967 to 2011. Of 109 cases with IVC anomalies identified by the literature search, 22 cases (20.2%) displayed no interiliac anastomosis. The interiliac vein connecting duplicated IVC existed in 74 cases (67.9%). According to the running direction of the interiliac vein, we found that the vein ran from left to right in 42 cases, coursed from right to left in 19 cases, and ran horizontally in 13 cases. Thirteen left IVC displayed symmetrical-to-normal connection with the bilateral common iliac veins. Awareness of these venous variations is necessary to reduce surgical risk and to determine strategy in interventional radiology.

Effects of aging on lateral stability in quiet stance.

BACKGROUND AND AIMS: Recent studies have demonstrated that assuming the postural corrective torque is regulated by a proportional-integralderivative (PID) controller in the anterior/posterior direction, although few studies have discussed the medial/ lateral (M/L) direction through PID control. Instability in the M/L direction has been reported to be closely related with the risk of falling in the elderly. The purpose of this study is to evaluate the mechanism of postural control in the M/L direction in the elderly. METHODS: The movement of a marker on the subject's back was measured by a CMOS video camera and trunk sway speeds in the M/L direction (TSSX) were calculated as absolute values in whole time series. Using trunk sway data, we identified the gain of PID parameters (proportional gain: KP, integral gain: KI derivative gain: KD). In addition, we calculated the frequency spectrum of trunk sway using the marker locus from 0.016 to 5 Hz by fast Fourier transform. A total of 40 healthy subjects aged from 20 to 85 years old was evaluated with the PID control algorithm in a model of postural control in the M/L direction and their parameter values were estimated. RESULTS: KP significantly increased with age, whereas KD tended to decrease. The TSSX and power ratio of medium frequency (0.2-2.0 Hz) significantly increased with age, but the power ratio of low frequency (0.02-0.2 Hz) tended to decrease. KP and KI were significantly correlated with the power ratio of medium frequency. There was a significant negative correlation between KD and TSSX. CONCLUSIONS: Our results indicate that dependence on hip and ankle stiffness, which may be controlled by proportional gain, increases with age for postural control in the M/L direction. A disability in the feedback mechanism based on velocity information for postural control, which may be associated with derivative gain, tends to increase with age but shows considerable individual variation.

Pronounced muscle deoxygenation during supramaximal exercise under simulated hypoxia in sprint athletes.

The purpose of this study was to determine whether acute hypoxia alters the deoxygenation level in vastus lateralis muscle during a 30 s Wingate test, and to compare the muscle deoxygenation level between sprint athletes and untrained men. Nine male track sprinters (athletic group, VO2max 62.5 ± 4.1 ml/kg/min) and 9 healthy untrained men (untrained group, VO2max 49.9 ± 5.2 ml·kg(-1)·min(-1)) performed a 30 s Wingate test under simulated hypoxic (FIO2 = 0.164 and PIO2 = 114 mmHg) and normoxic conditions. During the exercise, changes in oxygenated hemoglobin (OxyHb) in the vastus lateralis were measured using near infrared continuous wave spectroscopy. Decline in OxyHb, that is muscle deoxygenation, was expressed as percent change from baseline. Percutaneous arterial oxygen saturation (SpO2), oxygen uptake (VO2), and ventilation (VE) were measured continuously. In both groups, there was significantly greater muscle deoxygenation, lower SpO2, lower peakVO2, and higher peakVE during supramaximal exercise under hypoxia than under normoxia, but no differences in peak and mean power output during the exercise. Under hypoxia, the athletic group experienced significantly greater muscle deoxygenation, lower SpO2, greater decrement in peakVO2 and increment in peakVE during the exercise than the untrained group. When the athletic and untrained groups were pooled, the increment of muscle deoxygenation was strongly correlated with lowest SpO2 in the 30 s Wingate test under hypoxia. These results suggest that acute exposure to hypoxia causes a greater degree of peripheral muscle deoxygenation during supramaximal exercise, especially in sprint athletes, and this physiological response would be explained mainly by lower arterial oxygen saturation. Key pointsThe deoxygenation trends in the vastus lateralis muscle during 30 s Wingate test in track sprinters and untrained men under simulated hypoxic and normoxic conditions was investigated using near infrared spectroscopy.Acute hypoxia caused a greater degree of peripheral muscle deoxygenation than normoxia, whereas there were no changes in performance such as power output during 30 s Wingate test.Sprint athletes show a greater degree of peripheral muscle deoxygenation during 30 s Wingate test in hypoxia when compared with untrained subjects.A larger difference in muscle deoxygenation between hypoxia and normoxia is accompanied by lowest SpO2 at the 30 s Wingate test in hypoxia.