Here is an interesting article:
Acute Stroke Phase Voluntary Cough and Correlation with Maximum Phonation Time American Journal of Physical Medicine & Rehabilitation – June 2012, Volume 91, Issue 6, pp 494-500
Objective: This study aimed to assess cough effectiveness after a stroke and to propose a bedside screening test.
Design: Patients who had ischemic hemispheric stroke were recruited and followed up for 2 mos. Maximum phonation time (MPT) was assessed during the first 10 days. Aspiration was evaluated on days 2 and 10 after stroke. Lung function testing was performed on day 10. Peak cough flow less than 160 liters/min was defined as the criterion for cough ineffectiveness. Correlation between peak cough flow and MPT was determined, and the optimal cutoff value relating MPT to effective cough was determined using receiver operating characteristic analysis when referring to peak cough flow.
Results: Of the 70 patients, 6 developed pneumonia (mean time, 1.7 ± 2.4 days). Lung function assessment in 32 cases revealed general reduced cough effectiveness. MPT was correlated with peak cough flow (r = 0.413, P = 0.025), and an MPT cutoff of 10 secs was identified. Forty-seven patients were able to perform MPT on day 2; 49 were able to perform on day 10. Patients with MPT of 10 secs or longer had less frequent aspiration on both day 2 (5.9% vs. 36.7%, P = 0.034) and day 10 (2.9% vs. 26.6%, P = 0.026).
Conclusions: Cough effectiveness was reduced at the time of greatest risk for pneumonia. MPT provides a reliable bedside screening test of cough effectiveness.