Although heart rate varied little between Exacerbation Levels II to III, it is important to note that it was substantially elevated in patients ( Figure 3A ) with the clearest difference being between in-and out-patients. This is possibly associated with the anxiety and dyspnea that experienced when an exacerbation occurs. The increase in heart rate of course increases the oxygen requirements of the heart. The increased heart rate may also be the result of underlying cardiovascular disease that is more prominent in severe COPD patients [43] .