Inflated cuff pressure significantly alters pulse waveform shape acquired by brachial cuff volume displacement technique

Blood pressure waveform features and non-invasive central pressure estimation are increasingly used in research and clinical environments. Brachial cuff based biomedical devices often use an arbitrary absolute cuff pressure to measure waveforms. That is, cuff pressure is not relative to a person’s own blood pressure. This may alter the measured waveform shape, changing outcomes. This study investigates the impact of cuff pressure on pulse waveform shape. Supine brachial systolic, diastolic, and true mean blood pressure was measured in 14 healthy volunteers (age 25 to 60 years, 2 female) using the oscillometric technique. Brachial volume pressure pulse was measured using a standard brachial cuff inflated to: 10 mmHg below diastolic pressure (subdiastolic); mean pressure; 10 mmHg above systolic pressure (suprasystolic). At each cuff pressure, 10 seconds of data was acquired (sampling rate 2 kHz, 0.2 second Bartlett smoothing window) and averaged to form a single pulse waveform. Waveform shape was quantified in terms of form factor ((mean– diastolic pressure)/pulse pressure), normalised root mean square (RMS), and frequency components. Waveforms acquired at each cuff pressure, the radial artery pressure waveform acquired by tonometry, and form factor calculated from brachial oscillometric blood pressure values were statistically compared. Form factor was significantly different (p‹0.001) between subdiastolic (0.56±0.04), mean pressure (0.49±0.05) and suprasystolic (0.24±0.03) cuff pressures. This was also significantly different (p‹0.001) to form factor acquired by oscillometric method (0.33±0.02) and radial tonometry (0.32±0.03). Oscillometric brachial and tonometric radial form factor was not significantly different (p‹0.64). Normalised RMS values did not differ between suprasystolic (0.41±0.04) and radial tonometry (0.42±0.03) but were significantly different (p‹0.001) between suprasystolic, mean pressure (0.59±0.03) and subdiastolic (0.64±0.03) values. Frequency decomposition confirmed the quantified waveform shape differences. Therefore, different inflated cuff pressures relative to a person’s own blood pressure significantly alter the recorded pulse waveform shape and the outcomes based on those waveforms.