Peripheral arterial tone as an on-line measure of load in a simulated flight task.

Variations in continuous and discrete flight demands were investigated in a simulated flight mission measuring peripheral arterial tone (PAT) from the tip of the finger. A total of 12 participants performed a computer-simulated agricultural flight task. They were required to fly over a specific lane of a simulated corn field (continuous task) and change lanes in response to flags, which appeared at varying intervals (discrete task). The difficulty of the flight task was manipulated by varying the airplane control (single- vs. dual-axis control), while the difficulty of the discrete task was manipulated by varying the amount of lateral change signalled by the flag. PAT amplitude was lower in the difficult level of the continuous task and was further attenuated following the appearance of the flag only when a change in the flight position was required. These results suggest the potential utility of PAT as an on-line measure of the joint continuous and discrete demands of a flight mission.

Hydroxyurea and periodicity in myeloproliferative disease.

Three patients, one with polycythaemia vera (PV) and two with chronic myeloid leukaemia (CML), are described who had cycling of blood counts which became apparent whilst receiving hydroxyurea therapy. Significant periodicity was confirmed with the use of the Lomb periodogram. This is Fourier power spectral analysis tailored for unevenly sampled data. The patient with PV had marked oscillations of platelet counts with a periodicity of 29 d and an amplitude of (202-588)x10(9)/L. Smaller oscillations of neutrophil, monocyte and lymphocyte numbers and Hb levels occurred with a similar periodicity. Anticipatory changes in hydroxyurea dosage or the maintenance of a constant dose did not abolish periodicity, but a change in therapy to the non-cycle-specific drug anagrelide dampened and abolished the cycling. One of the patients with CML had tremendous and clear oscillations in white cell, platelet and Hb levels, with a mean periodicity of 74 d. The other had erratic counts which were confirmed to be significantly periodic (64 d), on spectral analysis. A change in therapy to busulphan in both these patients again dampened and abolished the cycling. Hydroxyurea, which is a cell-cycle-specific agent, probably exacerbates the periodicity which may be present in some patients with myeloproliferative disease. A change in therapy to non-cycle-acting compounds such as busulphan or anagrelide results in much more stable counts in such patients.