W. J. Gibbons

Reference values for a multiple repetition 6-minute walk test in healthy adults older than 20 years

PURPOSE To (1) identify greatest 6-minute walk distance (6MWD) from among several repetitions (best 6MWD) in a wide age range of healthy volunteers to develop reference values for the multiple repetition 6MWD, and (2) investigate the influence of demographics, anthropometrics, and habitual exercise activity on best 6MWD. METHODS Four 6MWD were performed on the same day in a 20-meter corridor by 41 male and 38 female healthy volunteers ranging in age from 20 to 80 years. The greatest 6MWD by each subject from among four 6MWDs was the primary outcome measure. RESULTS Eighty-six percent had their best 6MWD after the first walk; an average increase of 43 meters was observed from first to best 6MWD (P < 0.003). Best 6MWD averaged 698 +/- 96 meters and was inversely related to age (P < 0.001), directly to height (P < 0.001), and was greater in men than women (P < 0.0002). A regression model accounted for 41% of between-subject variability in best 6MWD (P < 0.00000001). In a subset of older subjects, predicted 6MWD significantly underestimated measured best 6MWD when reference values were used from another study where test familiarization was not provided, but this difference disappeared when value were used from the present and a third study where test familiarization was provided. CONCLUSIONS The present study is the first to provide predicted 6MWD values performed with multiple repetitions and for subjects in the 20-40-year-old age range. Selection of appropriate predicted 6MWD values for interpretation of performance should be guided by subject age and degree of test familiarization provided.

Optimization of Respiratory Muscle Relaxation during Mechanical Ventilation

The authors calculated the active work of inspiration (Wp) and the inspiratory muscle pressure-time product (∫ Pmus · dt) in seven patients undergoing mechanical ventilation (M V). This was done by comparing the areas under the inflation pressure-volume and inflation pressure-time curves generated when the patient was contributing to the work of ventilation with those following sedation, when inspiratory muscle activity was absent (defined as absence of diaphragmatic EMG activity and of palpable accessory muscle contraction). Inspiratory muscle inactivity could be predicted by the observation of a smooth rise in inflation pressure that was highly reproducible from breath to breath. Relaxation was present without sedation during MV in the control mode with inspiratory flow rates above 65 1/min. In the assist mode (AMV), both Wp and ∫ Pmus · dt were significantly (P < 0.05) greater than in the control (CMV) mode. Reducing trigger sensitivity during AMV further increased Wp and ∫ Pmus·dt (P < 0.05). During AMV and CMV Wp and ∫ Pmus · dt decreased with increasing rate of inspiratory flow delivered by the ventilator. With AMV at low trigger sensitivity and low flow rates, Wp approached 65% of the total inspiratory work. The authors conclude that inspiratory muscle activity can be substantial during MV, particularly during AMV at low trigger sensitivity and flow. Monitoring of inflation pressure is a simple means of determining the degree of inspiratory muscle rest during MV.

Iatrogenic “buffalo chest” bilateral pneumothoraces following unilateral transbronchial lung biopsies in a bilateral lung transplant recipient

We present a 54 year old male patient who had a bilateral lung transplant sixteen years ago for Alpha-1 Antitrypsin Deficiency-related emphysema. He was referred for flexible bronchoscopy with transbronchial biopsies to evaluate new mild exertional dyspnea and worsening of his FEV1. Eight transbronchial biopsies were done from the right middle lobe and the right lower lobe. Post procedure he developed bilateral pneumothoces that required emergent bilateral pleural ‘pigtail’ catheters. To our knowledge, this is the first reported case of bilateral pneumothoraces that developed after a unilateral procedure in a bilateral lung transplant recipient relatively late after the transplant.