Mechanisms of Arterial Hypotension in Chronic Spinal Cord Injury

Methods & Procedures

Screening spirometry will be performed with patient sitting in his/her personal wheelchair using BreezeSuite System. Forced Vital Capacity (FVC) & Forced Expiratory Volume in 1 second (FEV1) will be obtained & expressed as the percent of the predicted value for each subject based on a database of neurologically intact individuals with no known pulmonary complaints that was derived based on gender, age, & height. Three acceptable spirograms will be obtained & the result of their best attempt will be used.

Screening Orthostatic Stress Test will be conducted in patient placed on the cardiac chair (Chair Hydraulics). The left hand will be placed in an arm sling & kept at the level of the heart throughout the study. Continuous beat-to beat arterial blood pressure will be acquired from a finger cuff placed around the left middle or index finger (Portapres-2) in supine position & when the participants is moved into the upright seated position. Supine positions will be maintained for 15 min. & upright position will be maintained for 5 min. Baseline values in supine position will be recorded during the last 5-min period just before changing to the upright position. This test will be aborted if subjects become lightheaded or symptomatic of syncope.

Spirometry & Respiratory Muscle Strength Tests: Standard spirometry will be performed in sitting position by using BreezeSuite System (MedGraphics). FVC & FEV1 will be obtained. MP45-36-871-350 Differential Pressure Transducer with UPC 2100 PC card & software (Validyne Engineering) will be used to measure the maximum inspiratory pressure (PImax) & the maximum expiratory pressure (PEmax) in sitting position. The PImax will be measured during maximal inspiratory effort beginning at near residual volume & PEmax will be measured during maximal expiratory effort starting from near total lung capacity. Subjects will be asked to use a three-way valve system with rubber tube as mouthpiece. The pressure meter incorporates a 1.5 mm diameter leak to prevent glottic closure & to reduce buccal muscle contribution during measurements. The assessment will require a sharp, forceful effort be maintained for a minimum of 2 seconds. The maximum pressure will be taken as the highest value that sustained for one second. The maximum value from three maneuvers that varied by less than 20% will be averaged. Participants will be given specific instructions prior to the test & will be verbally coached throughout the spirometry & respiratory muscle strength maneuvers.

Orthostatic Stress Test: