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Objective.To determine if an automatic algorithm using wavelet analysis techniques can be used to reliably determine respiratory rate from the photoplethysmogram (PPG). Methods.Photoplethysmograms were obtained from 12 spontaneously breathing healthy adult volunteers. Three related wavelet transforms were automatically polled to obtain a measure of respiratory rate. This was compared with a secondary timing signal obtained by asking the volunteers to actuate a small push button switch, held in their right hand, in synchronisation with their respiration. In addition, individual breaths were resolved using the wavelet-method to identify the source of any discrepancies. Results.Volunteer respiratory rates varied from 6.56 to 18.89 breaths per minute. Through training of the algorithm it was possible to determine a respiratory rate for all 12 traces acquired during the study. The maximum error between the PPG derived rates and the manually determined rate was found to be 7.9%. Conclusion.Our technique allows the accurate measurement of respiratory rate from the photoplethysmogram, and leads the way for developing a simple non-invasive combined respiration and saturation monitor.Objective.To determine if an automatic algorithm using wavelet analysis techniques can be used to reliably determine respiratory rate from the photoplethysmogram (PPG). Methods.Photoplethysmograms were obtained from 12 spontaneously breathing healthy adult volunteers. Three related wavelet transforms were automatically polled to obtain a measure of respiratory rate. This was compared with a secondary timing signal obtained by asking the volunteers to actuate a small push button switch, held in their right hand, in synchronisation with their respiration. In addition, individual breaths were resolved using the wavelet-method to identify the source of any discrepancies. Results.Volunteer respiratory rates varied from 6.56 to 18.89 breaths per minute. Through training of the algorithm it was possible to determine a respiratory rate for all 12 traces acquired during the study. The maximum error between the PPG derived rates and the manually determined rate was found to be 7.9%. Conclusion.Our technique allows the accurate measurement of respiratory rate from the photoplethysmogram, and leads the way for developing a simple non-invasive combined respiration and saturation monitor.

Objectives. To determine if wavelet analysis techniques can be used to reliably identify individual breaths from the photoplethysmogram (PPG). Methods. Photoplethysmograms were obtained from 22 healthy adult volunteers timing their respiration rate in synchronisation with a metronome. A secondary timing signal was obtained by asking the volunteers to actuate a small push button switch, held in their right hand, in synchronisation with their respiration. Each PPG was analyzed using primary wavelet decomposition and two new, related, secondary decompositions to determine the accuracy of individual breath detection. Results. The optimal breath capture was obtained by manually polling the three techniques, allowing detection of 466 out of the 472 breaths studied; a detection rate of 98.7% with no false positive breaths detected. Conclusion. Our technique allows the accurate capture of individual breaths from the photoplethysmogram, and leads the way for developing a simple non-invasive combined respiration and saturation monitor.

Harold Wilson. By Austen Morgan. London: Pluto Press, 1992. Pp.625; £25. ISBN 0 7453 0635 7Harold Wilson. By Ben Pimlott. London: Harper Collins, 1992. Pp.811; £20. ISBN 0 00 215189 8Tony Benn. A Biography. By Jad Adams. London: Macmillan, 1992. Pp.xv + 536; £20. ISBN 0 333 52258 2Media and Voters: The Audience, Content and Influence of Press and Television at the 1987 General Election. By William L. Miller. Oxford: Clarendon Press, 1991. Pp.xvii + 231; £30. ISBN 0 19 827377 0The Language of Political Leadership in Contemporary Britain. By John Gaffney. London: Macmillan, 1991. Pp.x + 257; £37.50. ISBN 0 333 53411 5The British Press and Broadcasting Since 1945. By Colin Seymour-Ure. Oxford: Basil Blackwell, 1991. Pp.xii + 269; £45 (hardback); £8.95 (paperback). ISBN 0 631 16443 X and 16444 8The Myth of the Blitz. By Angus Calder. London: Pimlico, 1992. Pp.302; £10. ISBN 0 7126 9820 5Les Anglais: Portrait of a People. By Philippe Daudy, translated and edited by Isabelle Daudy. London: Headline Book Publishing, 1992. Pp.424; £7.99. ISBN 0 7472 3842 1Securing Peace in Europe, 1945-1962: Thoughts for the Post-Cold War Era. Edited by Beatrice Heuser and Robert O'Neill. London: Macmillan, 1992. Pp.xv + 345; £47.50. ISBN 0 333 55002 1Labour Governments and Private Industry: The Experience of 1945-1951 Edited by Helen Mercer, Neil Rollings and Jim Tomlinson. Edinburgh: Edinburgh University Press, 1992. Pp.244; £35. ISBN 0 7486 0339 5Education, Training and Economic Performance 1944-1990. By Derek H. Aldcroft. Manchester: Manchester University Press, 1992. Pp.196; £35 ISBN 0 7190 3460 4Culture in Britain Since 1945. By Arthur Marwick. Oxford: Basil Blackwell, 1991. Pp.206; £8.95. ISBN 0 631 17191 6Cultural Revolution? The Challenge of the Arts in the 1960s. Edited by Bart Moore-Gilbert and John Seed. London: Routledge, 1992. Pp.287; £35. ISBN 0 415 07824 5The Middle Classes 1900-1950. By Alan A Jackson. Melksham: David St John Thomas Publisher, 1991. Pp.353; £22.50. ISBN 0 946537 67 4British Cabinet Government. By Simon James. London: Routledge, 1992. Pp.ix + 271; £35 (hardback); £12.99 (paperback). ISBN 0 415 076056 and 07606 4

In order to describe the dynamics of a group of road vehicles travelling in a single lane, car-following models attempt to mimic the interactions between individual vehicles where the behaviour of each vehicle is dependent upon the motion of the vehicle immediately ahead. In this paper we investigate a modified car-following model which features a new nonlinear term which attempts to adjust the inter-vehicle spacing to a certain desired value. In contrast to our earlier work, a desired time separation between vehicles is used rather than simply being a constant desired distance. In addition, we extend our previous work to include a non-zero driver vehicle reaction time, thus producing a more realistic mathematical model of congested road traffic. Numerical solution of the resulting coupled system of nonlinear delay differential equations is used to analyse the stability of the equilibrium solution to a periodic perturbation. For certain parameter values the post-transient response is a chaotic (non-periodic) oscillations consisting of a broad spectrum of frequency components. Such chaotic motion leads to highly complex dynamical behaviour which is inherently unpredictable. The model is analysed over a range of parameter values and, in each case, the nature of the response is indicated. In the case of a chaotic solution, the degree of chaos is estimated.