Method and apparatus for detecting optical pulses

Improved apparatus for detecting arterial pulses of a patient comprising:

• means for photoelectrically detecting the blood flow, which may include arterial pulses and artifacts, at the body tissue;
• means for detecting the electrical heart activity of the patient in the form of an EKG waveform;
• circuit means for filtering and processing the EKG waveform to detect a selected component of the EKG waveform, so that the occurrence of that selected component represents the occurrence of a heartbeat;
• means for correlating detected arterial pulses with the occurrence of the heartbeat, said correlating means being adapted to establish a time period by which a detected arterial pulse is likely to follow the occurrence of a selected component of the EKG waveform;
• and
• means for confirming whether or not a detected pulse is likely to be an arterial pulse, said confirming means being responsive to the detected arterial pulse and a detected heartbeat and adapted to confirm that a detected pulse is acceptable as an arterial pulse by determining that the detected pulse occurs within the established time period.

A method for photoelectrically measuring the amount of a blood constituent from the blood flow characteristics in the body tissue of a patient using a device that is transmitting light through the body tissue, detecting and converting the amount of light transmitted from analog blood flow signals having arterial pulses and artifacts to digital signals, comprising:

• digitally processing the digital signals to detect arterial pulses and determine an arterial pulse rate and the amount of a blood constituent present in the arterial blood;
• detecting the patient's EKG waveform having a selected component corresponding to the onset of a heartbeat;
• converting the EKG waveform into a digital EKG waveform having a digital heart pulse corresponding to each occurrence of the selected component of the EKG waveform, determining a digital heart pulse rate, comparing the digital EKG waveform and digital heart pulse rate to the digital signals and the arterial pulse rate to establish a time period by which an arterial pulse follows the occurrence of a digital heart pulse as the period of time after the occurrence of a digital heart pulse when it is likely that an arterial pulse will be detected;
• and
• thereafter digitally processing the digital signals detected during the established time period to determine the amount of a blood constituent present in the blood.

An improved non-invasive device for measuring the amount of blood constituents in body tissue of a patient by photoelectrically detecting changes in blood flow characteristics having arterial pulses and artifacts in the form of digital signals, including a microprocessor, comprising:

• EKG circuit means for detecting the EKG waveform of the patient and generating a digital waveform having digital heart pulses that correspond to the occurrences of a selected portion of the EKG waveform;
• status input means for indicating when a selected portion of the EKG waveform has occurred, said status input means being associated with the microprocessor and responsive to the digital waveform of the EKG circuit means so that each digital heart pulse causes the status input means to indicate a selected portion of the EKG waveform has occurred;
• EKG signal processing means for calculating the EKG pulse rate, responsive to the EKG circuit means;
• means for analyzing the digital signals and the digital heart pulse waveform over several digital heart pulses, determining the typical time period by which an arterial pulse follows a digital heart pulse, and determining a time period as the period during which it is likely to find a digital signal pulse representative of an arterial pulse after the occurrence of a digital heart pulse, said means being associated with the microprocessor and the EKG signal processing meas;
• and
• microprocessor means for analyzing digital signals detected during the determined time period after the occurrence of a digital heart pulse, said microprocessor means being responsive to the determined time period and the digital waveform so that calculations of the amount of the blood constituent will be based on those portions of the changes in the blood flow characteristics detected during the determined time period.

A method for calculating the amount of blood constituent from the blood flow characteristics of a patient comprising:

• detecting an absorption signal corresponding to the absorption of light in the patient's tissue including periodic changes caused by periodic arterial pulses in the blood flow characteristics and changes caused by artifact;
• detecting an EKG signal corresponding to the patient's EKG waveform including a selected portion of the EKG waveform corresponding to the periodic electrical heart activity of the patient;
• correlating the detected absorption and EKG signals by determining a time relationship between the EKG and absorption signals to determine a time delay by which changes in the absorption signal corresponding to arterial pulses are likely to be detected after an occurrence of the selected portion of the EKG waveform;
• processing the absorption signal and the determined correlation to identify the periodic changes in the absorption signal likely to correspond to arterial pulses in the patient's blood flow characteristics by using the determined time relationship and the determined time delay to determine a time window when the probability is high that a detected change in the absorption signal corresponds to an arterial pulse;
• and
• calculating the amount of the blood constituent from the identified periodic changes in the absorption signal by using the occurrences of the selected portion of the EKG waveform and the determined time window to identify the periodic changes in the absorption signal likely to correspond to arterial pulses.

An apparatus for use in calculating the amount of a blood constituent from the blood flow characteristics of a patient comprising:

• means for photoelectrically detecting an absorption signal corresponding to the absorption of light in the patient's tissue including periodic changes caused by periodic arterial pulses in the blood flow characteristics and changes caused by artifacts;
• means for electrically detecting an EKG signal corresponding to the patient's EKG waveform including a selected portion of the EKG waveform corresponding to the periodic electrical heart activity of the patient;
• first processing means for correlating the detected absorption and EKG signals by processing the absorption and EKG signals and determining a time relationship between the absorption and EKG signals to determine a time delay by which a change in the absorption signal corresponding to an arterial pulse is likely to be detected after the occurrence of a selected portion of the EKG waveform and processing the determined time relationship and the determined time delay to calculate a time window when the probability is high that a detected change in the absorption signal corresponds to an arterial pulse;
• second processing means for processing the absorption signal and the determined correlation by processing the absorption signal using the occurrences of the selected portion of the EKG waveform and the determined time window to identify the periodic changes in the absorption signal likely to correspond to arterial pulses in the patient's blood flow characteristics;
• and
• means for calculating the blood constituent from the identified periodic changes in the absorption signal.