Much telemonitoring is prerecorded since there is often no need for a real-time link. Real-time data transfer is indicated only if an immediate response is required. Real-time transfer is used for teleconsultation in cardiology patients or other urgent cases. Data can be transferred over the ordinary public telephone network using a modem or by fax. Data can also be transferred by mobile phone. Increasingly, the Internet is used as part of the communication pathway.
Modem: Data transmission by modem has been used for real-time blood pressure and real-time ECG monitoring of patients at home. ECG transmission has also been demonstrated from ambulances, using transmission via the mobile phone network. ECG monitoring from ﬁxed locations has passed from the experimental stage to become a routine telecardiology service, with cardiac call centers set up to provide an immediate opinion from a cardiologist.
Fax: Fax machines can be used to transfer paper records, such as ECG recordings. However, the good-quality transmission of ECG traces is difficult without taking special precautions to digitize the recording appropriately. A fax machine was used to transmit surgical diagrams in a rural emergency to coach a rural general practitioner to perform a life-saving procedure.
Mobile phone: The advantage of data transmission by ﬁxed telephone line is that it can take place at rates of some 35 Kbps and access to the telephone network is possible from almost anywhere in the world. Data transmission is also possible using a mobile phone, albeit at lower transmission rates and from more restricted areas. The key advantage is mobility. Successful telemedicine has been carried out for cardiology, in which an ECG was transmitted to a mobile phone with a built-in display.